Differences in the catalytic efficiencies of allelic variants of glutathione transferase P1-1 towards carcinogenic diol epoxides of polycyclic aromatic hydrocarbons

Recently, we found a 13-lipoxygenase in germinating cucumber cotyledons, which was located at the lipid body membrane. Based on its products formed mobilization of storage lipids seems to be initiated by this 13-lipoxygenase. For biochemical characterization its cDNA was expressed as His-tagged protein. Active recombinant enzyme was obtained from low temperature cultivation of E. coli after affinity purification. It (i) exhibited an unchanged region specificity, and (ii) showed a pH optimum of 7.2 against trilinolein as substrate. We compared its ability to oxygenate trilinolein with the one of another 13-lipoxygenase, soybean lipoxygenase-1. At the pH optimum of soybean lipoxygenase-1 (9.0), trilinolein was oxygenated only to 28% of the amount converted by the lipid body lipoxygenase. Moreover, trilinolein oxygenation by soybean lipoxygenase-1 leads mainly to monohydroperoxy derivatives, whereas oxygenation by lipid body LOX leads to a trihydroperoxy derivative.     

Linoleic acid peroxidation by Solanum tuberosum lipoxygenase was activated in the presence of human 5-lipoxygenase-activating protein

The present investigation describes the ability of human 5-lipoxygenase-activating protein (FLAP) to activate a plant 5-lipoxygenase. The presence of an active recombinant human FLAP in the 100000xg membrane fraction of infected Sf9 cells led to a specific increase in 9-hydroperoxyoctadecadienoic acid (9-HPOD) synthesis (+68%) or in 5-hydroperoxyeicosatetraenoic acid (5-HPETE) synthesis (+68%), after action of Solanum tuberosum tuber 5-lipoxygenase (S.t.LOX) on linoleic acid (natural plant lipoxygenase substrate) or on arachidonic acid. On the contrary, the presence of non-transfected membranes obtained from non-infected Sf9 cells led to an inhibition of lipoxygenase activity. MK-886, a potent inhibitor of leukotriene biosynthesis, blocked the FLAP dependent S.t.LOX activation after preincubation with FLAP transfected membranes. In conclusion, this study demonstrates that a recombinant human FLAP can stimulate a lipoxygenase other than mammalian 5-lipoxygenase (S.t.LOX) by using different polyunsaturated fatty acids as substrates.     

Fine chemical modifications at N- and C-termini enhance peptide presentation to T cells by increasing the lifespan of both free and MHC-complexed peptides

We investigated the effect of modifying the N- and/or C-termini of the snake toxin peptide 24-36 on its presentation to T cells. Acetylation at the N-terminus as well as amidation at the C-terminus enhanced the capacity of the peptide to activate T cells. Simultaneous modifications further increased the stimulating activity, the peptide becoming approximately 100-fold more potent than the unmodified peptide. Clearly, the introduced modifications increased the lifetime of the peptide free in solution, by decreasing its proteolytic degradation, during the T cell stimulation assays. Paradoxically, however, at similar concentrations of free peptides, the modified ones, especially those having an acetylated N-terminus, were much more active than the unmodified peptide, irrespective of the experimental conditions. These observations suggested that components other than protection from proteolytic degradation should be associated with the higher stimulating activities of the modified peptides. Accordingly, chasing experiments with APC revealed that acetylation at N-terminus caused a higher persistence of the peptides at APC surface. Together, our data indicate that (i) the T cell stimulating capacity of a peptide is associated with its lifespans in the free and MHC II bound states; and (ii) these lifespans can be greatly enhanced by introducing fine chemical modifications at N- and C-termini. These data may have some implications in designing more potent peptidic immunomodulators.     

Purification and characterization of a mannose/glucose-specific lectin from Castanea crenata

A hemagglutinin was purified from the cotyledons of Japanese chestnut (Castanea crenata Sieb. et Zucc.) by affinity chromatography on asialo-fetuin Sepharose 4B column followed by anion-exchange and gel permeation chromatography. The hemagglutinating activity of Castenea crenate agglutinin (CCA) was strong for sialidase-treated human erythrocytes, but was inhibited by mannose, glucose, and their derivatives as well as by glycoproteins having an N-linked complex carbohydrate type. The apparent M(r) of intact CCA was determined to be ca 257,000 by gel filtration using a Superose 12 column. In SDS-PAGE, under reducing and non-reducing conditions, CCA migrated as a single band of M(r) 37,000. Therefore, the intact CCA may be composed of six or eight identical subunits without disulfide bonds. In addition, CCA showed strong mitogenic activity similar to other lectins. The N-terminal amino acid of CCA may be blocked since no amino acid was detected by direct sequence analysis. Amino acid analysis showed that CCA was rich in glycine, but did not contain cysteine residues. Some properties of CCA were similar to mannose/glucose-specific legume lectins, but our data suggest that the molecular structure of CCA is different.     

Selenoenzymes regulate the activity of leukocyte 5-lipoxygenase via the peroxide tone

The variation of the selenium status of leukocytes was used as a tool to investigate the influence of selenium-containing glutathione peroxidases on the formation of 5-lipoxygenase metabolites in vitro and ex vivo. Selenium-deficient rat basophilic leukemia cells had < 1% of control glutathione peroxidase activity and 35% of control phospholipid hydroperoxide-glutathione peroxidase activity. Upon stimulation, these cells released an 8-fold amount of lipoxygenase metabolites compared to controls. No (5S)-hydroperoxyeicosatetraenoic acid was detectable in whole cells; however, it was found in homogenates of selenium-deficient cells. Addition of 0.25 microgram/ml selenium to selenium-deficient cells restored control phospholipid hydroperoxide-glutathione peroxidase activity within 8 h, whereas glutathione peroxidase activity needed 7 days. 12 h after resupplementation, selenium-deficient cells had 3% glutathione peroxidase and 100% phospholipid hydroperoxide-glutathione peroxidase activity compared to controls. Resupplemented cells released control amounts of 5-lipoxygenase metabolites, indicating that restoration of phospholipid hydroperoxide-glutathione peroxidase activity is associated with a selenium-adequate leukotriene metabolism. Leukocytes that were isolated from selenium-deficient rats released a 7-fold amount of total lipoxygenase metabolites compared to cells from control animals. By injecting normally fed rats with 500 micrograms/kg selenium as Na2SeO3, leukocyte phospholipid hydroperoxide-glutathione peroxidase activity was raised 8-fold within 114 h compared to controls. Leukocytes from these animals produced significantly less lipoxygenase metabolites than controls. These findings indicate that phospholipid hydroperoxide-glutathione peroxidase activity is primarily responsible for the reduction of 5-hydroperoxyeicosate-traenoic acid and therefore governs the actual activity of leukocyte 5-lipoxygenase via regulating the tone of endogenous hydroperoxides.     

Platelet lipoxygenase in spontaneously hypertensive rats

We have previously reported that the nonselective lipoxygenase inhibitor phenidone is a potent hypotensive agent in the spontaneously hypertensive rat (SHR). In the present study, we examined the relationship between production of platelet 12-hydroxyeicosatetraenoic acid (12-HETE) and intra-arterial blood pressure in SHR and Wistar-Kyoto rats (WKY) using both a cross-sectional analysis and an acute pharmacological intervention. Basal generation rate of 12-HETE by platelets collected from the SHR was approximately 3.7-fold higher than in the WKY (0.86 +/- 0.24 versus 0.23 +/- 0.05 nmol/mL per 10 minutes, respectively; P < .01). Systolic arterial pressure was positively related to platelet 12-HETE formation rate when the entire rat population was considered (r = .70, P < .001). The specific 12-lipoxygenase inhibitor cinnamyl-3,4-dihydroxycyanocinnamate induced lowering of both arterial blood pressure and platelet 12-lipoxygenase activity in SHR. At 15 mg/kg, cinnamyl-3,4-dihydroxycyanocinnamate elicited a marked hypotensive effect in SHR but not in WKY. This reduction in arterial pressure was accompanied by an approximate 70% inhibition in platelet 12-HETE production rate. The return of high blood pressure to basal levels was associated with a significant rise in the production of platelet 12-HETE toward control values (baseline, 0.97 +/- 0.33 nmol/mL per 10 minutes; nadir of blood pressure, 0.19 +/- 0.03; resumption of basal pressure, 0.42 +/- 0.14). In contrast, captopril (15 mg/kg) induced a quantitatively similar decrease in blood pressure but had no effect on platelet 12-HETE generation rate. Thus, hypertension in SHR is linked to increased production rate of platelet 12-HETE. Acute blood pressure reduction attained during lipoxygenase inhibition but not by angiotensin converting enzyme inhibition leads to a concomitant reduction in the production of platelet 12-HETE. We speculate that since rat arterial tissue produces 12-HETE, increased 12-lipoxygenase activity in SHR may contribute to the maintenance of elevated arterial pressure in this strain.     

Calpain-calpastatin interactions in epidermoid carcinoma KB cells

We examined the activation of mu-calpain in human epidermoid carcinoma KB cells following a rise in intracellular calcium concentration using antibodies specifically recognizing different activation states of mu-calpain. KB cells possess calpastatin activity in large excess of calpain activity as analyzed by ion exchange HPLC. Stimulation of the cells with a calcium ionophore, ionomycin, caused production of the autolytic intermediate form (M(r) = 78 k) of mu-calpain derived from the preautolysis form (80 k), while the fully autolyzed postautolysis form (76 k) remained below detectable levels at all times. The appearance of the autolytic intermediate paralleled limited proteolysis of the membrane-associated calpastatin fractions (110 k and 106 k); the resulting fragments (68 k and 45 k) were released into the cytosol. Both the production of the autolytic mu-calpain intermediate and the limited proteolysis of calpastatin in cell lysates in the presence of calcium were inhibited by a synthetic calpastatin peptide, indicating that proteolysis of calpastatin was indeed catalyzed by calpain and that the autolytic intermediate may have exerted the proteolytic activity. Furthermore, mu-calpain autolysis and calpastatin degradation, upon ionomycin treatment, were both augmented by epidermal growth factor (EGF). These results suggest that calpastatin serves not only as an inhibitor but also as a substrate for calpain at cell membranes and that intracellular conditions associated with the cell cycle may affect the activation of mu-calpain.     

Expression of Alzheimer's disease-associated presenilin-1 is controlled by proteolytic degradation and complex formation

Numerous mutations causing early onset Alzheimer's disease have been identified in the presenilin (PS) genes, particularly the PS1 gene. Like the mutations identified within the beta-amyloid precursor protein gene, PS mutations cause the increased generation of a highly neurotoxic variant of amyloid beta-peptide. PS proteins are proteolytically processed to an N-terminal approximately 30-kDa (NTF) and a C-terminal approximately 20-kDa fragment (CTF20) that form a heterodimeric complex. We demonstrate that this complex is resistant to proteolytic degradation, whereas the full-length precursor is rapidly degraded. Degradation of the PS1 holoprotein is sensitive to inhibitors of the proteasome. Formation of a heterodimeric complex is required for the stability of both PS1 fragments, since fragments that do not co-immunoprecipitate with the PS complex are rapidly degraded by the proteasome. Mutant PS fragments not incorporated into the heterodimeric complex lose their pathological activity in abnormal amyloid beta-peptide generation even after inhibition of their proteolytic degradation. The PS1 heterodimeric complex can be attacked by proteinases of the caspase superfamily that generate an approximately 10-kDa proteolytic fragment (CTF10) from CTF20. CTF10 is rapidly degraded most likely by a calpain-like cysteine proteinase. From these data we conclude that PS1 metabolism is highly controlled by multiple proteolytic activities indicating that subtle changes in fragment generation/degradation might be important for Alzheimer's disease-associated pathology.     

A function for lipoxygenase in programmed organelle degradation

Membrane-enclosed organelles, a defining characteristic of eukaryotic cells, are lost during differentiation of specific cell types such as reticulocytes (an intermediate in differentiation of erythrocytes), central fibre cells of the eye lens, and keratinocytes. The degradation of these organelles must be tightly regulated with respect to both the time of activation and the specificity of membrane degradation. The expression of 15-lipoxygenase (15-LOX) peaks in reticulocytes immediately before organelle degradation. Here we show that 15-LOX integrates into the membranes of various organelles, allowing release of proteins from the organelle lumen and access of proteases to both lumenal and integral membrane proteins. In addition, by sparing the plasma membrane, 15-LOX shows the required specificity for organellar membranes. Thus, the action of 15-LOX provides a mechanism by which the natural degradation process can be explained. This conclusion is supported by our finding that lipoxygenase expression in the eye lens is restricted to the region at which organelle degradation occurs.     

Cloning of the gene for monogalactosyldiacylglycerol synthase and its evolutionary origin

Monogalactosyldiacylglycerol (MGDG) synthase (UDPgalactose:1,2-diacylglycerol 3-beta-D-galactosyltransferase; EC 2.4.1.46) catalyzes formation of MGDG, a major structural lipid of chloroplast. We cloned a cDNA for the synthase from cucumber cDNA library. The full-length cDNA clone was 2142 bp, and it contains a 1575-bp open reading frame encoding 525 aa. The open reading frame consists of the regions for a mature protein (422 aa; Mr of 46,552) and transit peptide to chloroplast (103 aa). Although the molecular weight of mature protein region matched that purified from cucumber cotyledons, it was quite different from those purified from spinach (approximately 20 kDa) reported by other groups. The mature region of the protein was expressed in Escherichia coli as a fusion protein with glutathione S-transferase. The expression in E. coli showed that the protein catalyzed MGDG synthesis very efficiently. Therefore, we concluded that the cDNA encodes MGDG synthase in cucumber. In addition, the deduced amino acid sequence of the MGDG synthase cDNA showed homology with MurG of Bacillus subtilis and E. coli, which encode a glycosyltransferase catalyzing the last step of peptidoglycan synthesis in bacteria. This sequence homology implies that the machinery of chloroplast membrane biosynthesis is evolutionarily derived from that of cell wall biosynthesis in bacteria. This is consistent with the endosymbiotic hypothesis of chloroplast formation.     

5-HPETE is a potent inhibitor of neuronal Na+, K(+)-ATPase activity

The effects of 1 microM concentrations of arachidonic acid hydroperoxide (HPETES) products of 5-, 12- and 15-lipoxygenase on Na+, K(+)-ATPase activity were investigated in synaptosomal membrane preparations from rat cerebral cortex. 5-HPETE inhibited Na+, K(+)-ATPase activity by up to 67 %. In contrast, 12-HPETE and 15-HPETE did not inhibit Na+, K(+)-ATPase activity. In addition, neither 5-HETE or LTA4 inhibited Na+, K(+)-ATPase activity. Dose-response studies indicated that 5-HPETE was a potent (IC25 = 10(-8) M) inhibitor of Na+, K(+)-ATPase activity. These findings indicate that 5-HPETE inhibits Na+, K(+)-ATPase activity by a mechanism that is dependent on the hydroperoxide position and independent of further metabolism by 5-lipoxygenase. It is proposed that 5-HPETE production by 5-lipoxygenase and subsequent inhibition of neuronal Na+, K(+)-ATPase activity may be a mechansim for modulating synaptic transmission.     

Arachidonate 15-lipoxygenase in human corneal epithelium and 12- and 15-lipoxygenases in bovine corneal epithelium: comparison with other bovine 12-lipoxygenases

Lipoxygenases of bovine and human corneal epithelia were investigated. The bovine epithelium contained an arachidonate 12-lipoxygenase and a 15-lipoxygenase. The 12-lipoxygenase was found in the microsomal fraction, while the 15-lipoxygenase was mainly present in the cytosol (100,000 x g supernatant). 12S-Hydroxyeicosatetraenoic acid (12S-HETE) and 15S-hydroxyeicosatetraenoic acid (15S-HETE) were identified by GC-MS and chiral HPLC. BW A4C, an acetohydroxamic acid lipoxygenase inhibitor, reduced the biosynthesis of 12S-HETE and 15S-HETE by over 90% at 10 microM. IC50 for the 12-lipoxygenase was 0.3 microM. The bovine corneal 12-lipoxygenase was compared with the 12-lipoxygenases of bovine platelets and leukocytes. All three enzymes metabolized 14C-labelled linoleic acid and alpha-linolenic acid poorly (5-16%) in comparison with [14C]arachidonic acid. [14C]Docosahexaenoic acid and [14C]4,7,10,13,16-docosapentaenoic acid appeared to be less efficiently converted by the corneal enzyme than by the platelet and leukocyte enzymes. Immunohistochemical analysis of the bovine corneal epithelium using a polyclonal antibody against porcine leukocyte 12-lipoxygenase gave positive staining. The cytosol of human corneal epithelium converted [14C]arachidonic acid to one prominent metabolite. The product co-chromatographed with 15S-HETE on reverse phase HPLC, straight phase HPLC and chiral HPLC. Our results suggest that human corneal epithelium contains a 15-lipoxygenase and that bovine corneal epithelium contains both a 15-lipoxygenase and a 12-lipoxygenase. The corneal 12-lipoxygenase appears to differ catalytically from earlier described bovine 12-lipoxygenases.     

Murine epidermal lipoxygenase (Aloxe) encodes a 12-lipoxygenase isoform

Using a combination of conventional screening procedures and polymerase chain reaction cloning, we have isolated a cDNA encoding an epidermis-type 12-lipoxygenase (e12-lipoxygenase) from mouse epidermis. The open reading frame corresponds to a protein of 662 amino acids and was found to be 99.8% identical to the ORF of an epidermal lipoxygenase gene Aloxe, described recently [Van Dijk et al. (1995) Biochim. Biophys. Acta 1259, 4-8]. When expressed in human embryonic kidney cells the recombinant protein could be shown to synthesize 12(S)-HETE from arachidonic acid. By fluorescence in situ hybridization the e12-lipoxygenase gene was localized to chromosome band 11 B1-B3.     

Identification of parvalbumin alpha in bovine hypothalamus: a partial primary structure

In the course of the study of structure-functional properties and molecular mechanisms of neuropeptides and of low molecular weight proteins of the central nervous system we succeeded in isolating from the soluble fraction of bovine hypothalamus a protein having M(r) 11897.3, according to mass spectral analysis. The purification procedure was mainly based on reversed phase HPLC. As the N-terminus of the molecule was found to be blocked, we have subjected it to CNBr degradation. By Edman microsequence analysis of the peptide fragments and by data base searching the isolated substance was identified as parvalbumin alpha (PRVA)-one of the calcium-binding proteins. However, its primary structure was found not to be identical to that of the known PRVAs from other sources. One of the features of PRVA is its stability. Being subjected to an exhausting purification procedure it retains its complete structure. As neuropeptides and low molecular weight proteins are found to be polyfunctional, a central question concerns the biological role of PRVAs in terms of "where and when" they express their action.     

Renal prostaglandins and thromboxane A2 lack a functional significance in the genesis of protein-induced glomerular hyperfiltration in human renal disease

Ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) was purified from an obligately autotrophic hydrogen-oxidizing bacterium, Hydrogenovibrio marinus MH-110. The protein has a M(r) value of approximately 110,000, and is composed of two identical subunits of 55,000. To our knowledge, the existence of L2-form RubisCO in a chemolithoautotrophic bacterium is first reported in this paper. The N-terminal amino acid sequence determination of the purified enzyme showed high homology with those of the L2-form RubisCO of Rhodospirillum rubrum and the Lx-form RubisCO from Rhodobacter sphaeroides.     

Proopiomelanocorticotropin (POMC) peptides and lipoprotein lipase activity in vitro

Effects of alpha-melanocyte-stimulating hormone (alpha-MSH), beta-melanocyte-stimulating hormone (beta-MSH), beta-lipotropin (beta-LPH), and beta-endorphin (beta-EPH) at concentrations from 10(-9) M up to 10(-6) M on human adipose tissue lipoprotein lipase (LPL) were studied in a cell-free system. alpha-MSH and beta-MSH did not exert any effect on LPL; no degradation of these peptides in the incubation medium could be detected by HPLC analysis. beta-LPH and beta-EPH failed to alter enzyme activity. However, HPLC analysis revealed an unspecific rapid degradation of the peptides due to the activity of tissue proteases. Therefore, the protease inhibitors amastatin, antipain, APMSF, and TPCK were tested at concentrations of 10(-5), 10(-4), and 10(-3) M for their efficacy to inhibit degradation. None of the inhibitors was able to substantially reduce proteolysis of beta-LPH, as was the case with amastatin, APMSF, and TPCK for beta-EPH. However, antipain at 10(-4) M preserved at least 20% of the initial peptide concentration from proteolysis up to 150 min. Antipain caused a decrease in lipoprotein lipase activity (LPLA), which was dependent on concentration. The adverse effect of antipain at concentrations of 10(-4) M on LPL was completely abolished by beta-EPH at a concentration of 10(-6) M.