Molecular requirements for T cell recognition by a major histocompatibility complex class II-restricted T cell receptor: the involvement of the fourth hypervariable loop of the Valpha domain

The role of two central residues (K68, E69) of the fourth hypervariable loop of the Valpha domain (HV4alpha) in antigen recognition by an MHC class II-restricted T cell receptor (TCR) has been analyzed. The TCR recognizes the NH2-terminal peptide of myelin basic protein (Ac1-11, acetylated at NH2 terminus) associated with the class II MHC molecule I-Au. Lysine 68 (K68) and glutamic acid 69 (E69) of HV4alpha have been mutated both individually and simultaneously to alanine (K68A, E69A). The responsiveness of transfectants bearing wild-type and mutated TCRs to Ac1-11-I-Au complexes has been analyzed in the presence and absence of expression of the coreceptor CD4. The data demonstrate that in the absence of CD4 expression, K68 plays a central role in antigen responsiveness. In contrast, the effect of mutating E69 to alanine is less marked. CD4 coexpression can partially compensate for the loss of activity of the K68A mutant transfectants, resulting in responses that, relative to those of the wild-type transfectants, are highly sensitive to anti-CD4 antibody blockade. The observations support models of T cell activation in which both the affinity of the TCR for cognate ligand and the involvement of coreceptors determine the outcome of the T cell-antigen-presenting cell interaction.     

Effects of iminodipropionitrile on cerebral amino acid levels

Iminodipropionitrile (IDPN), a compound that causes dyskinetic symptoms in animals and has possible use as a model for human dyskinesia, was tested in mice and rats for its effect on cerebral amino acids. In mice, 2 h after IDPN administration, the level of total brain alanine was reduced; after 5 h the levels of aspartic acid and glutamic acid were also reduced, and the level of glutamine was increased. In rats, after chronic administration of IDPN, the level of glutamic acid in the total brain tissue was reduced. After acute administration of IDPN using microdialysis, extracellular GABA and extracellular glutamine levels in the striatum were elevated. This study shows that IDPN causes alterations in total and extracellular levels of neurotransmitter amino acids in the brain, which could have a role in IDPN-induced dyskinesia.     

Postoperative mortality in infective endocarditis: determinant factors

OBJECTIVE: It has been shown recently that 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) is expressed as at least 2 isozymes. In the liver, 11 beta-HSD1 converts cortisone to cortisol; in the kidney, 11 beta-HSD2 converts cortisol to cortisone. Conventional assessment of 11 beta-HSD activity in vivo has relied on gas chromatographic measurement of the ratios of conjugated cortisol and cortisone metabolites. However, these do not permit distinction between the tissue-specific activities of the enzymes and do not reflect all forms of 11 beta-HSD deficiency. In this report, we have assessed the usefulness of measuring unconjugated cortisol metabolites and free cortisol and cortisone in urine as indices of renal 11 beta-HSD activity in man. DESIGN: Six healthy male subjects established in sodium balance were given either glycyrrhetinic acid (170 mg t.d.s., to inhibit 11 beta-HSD2), carbenoxolone (100 mg t.d.s., to inhibit both 11 beta-HSD1 and 11 beta- HSD2) or both inhibitors in combination. MEASUREMENTS: Urinary electrolytes were measured and the concentrations of total and unconjugated urinary cortisol and its metabolites were determined by gas chromatography mass spectrometry. RESULTS: Glycyrrhetinic acid and carbenoxolone inhibited renal 11 beta-HSD2 to a similar degree, as judged by similar sodium retention. As previously reported, conventional measurement of ratios of total cortisol to cortisone metabolites were influenced to a greater extent by glycyrrhetinic acid (100-200% increase in ratio from baseline) than by carbenoxolone (< 30% increase). However, the effect of carbenoxolone was readily detected by measurement of urinary unconjugated cortisol/cortisone (130-480% increase of ratio from baseline) and also by measurement of ratios of unconjugated cortisol metabolites (60-130% increase). CONCLUSIONS: Measurement of free cortisol and cortisone in urine provides the most sensitive index of renal 11 beta-HSD activity. Measurement of total and conjugated urinary steroids is insensitive in circumstances where 11 beta-HSD activity in liver or elsewhere may be abnormal.     

Discharge planning and community housing in Ontario

As hospital budgets in Ontario (and elsewhere) continue to shrink in the face of governmental fiscal pressure, bed closures lead to the discharge of increasingly vulnerable persons. Many of these persons have no family and no obvious place to go. Community supports to assist people outside the hospitals are not provided at a level commensurate with the need. The result is inadequate housing, social isolation, non-existent care and, in too many cases, reinstitutionalization and/or preventable deaths. This paper describes the process by which vulnerable adults wind up in unsuitable community settings, as a result of ill-conceived deinstitutionalization in the province of Ontario. It places a particular focus on the difficult role played by the discharge planner as conduit from hospital to community. The planner is often caught in the middle, facing hospital (and physician) directives to empty beds precipitously, alongside an acute shortage of suitable housing in the community. Departing patients are often sent to settings that lack any form of governmental inspection, regulation, licensure, or control: they are at the mercy of often indifferent and, at times, overtly rapacious landlords who may take the welfare cheque and give little in return. Selected case material, including one recent inquest, highlight the difficulties.     

Geranoyl-CoA carboxylase: a novel biotin-containing enzyme in plants

Geranoyl-CoA carboxylase (EC 6.4.1.4) is a biotin-containing enzyme previously described in two genera of bacteria. Here we report the presence of geranoyl-CoA carboxylase in kingdom Plantae. Geranoyl-CoA carboxylase was purified 180-fold from maize leaves. The enzyme has a biotin-containing subunit of 122 kDa. The pH optimum for activity is 8.3. The apparent Km values for the substrates geranoyl-CoA, bicarbonate, and ATP are 64 +/- 5 microM, 0. 58 +/- 0.04 mM, and 8.4 +/- 0.4 microM, respectively. Subcellular fractionations indicate that geranoyl-CoA carboxylase is located in plastids. Geranoyl-CoA carboxylase activity is ubiquitous in organs of monocots and dicots and varies with development. We postulate that geranoyl-CoA carboxylase plays an important role in isoprenoid catabolism in plants, in a pathway analogous to that shown in Psuedomonas sp. In plants, this catabolic pathway would require the interaction of at least three subcellular compartments (plastids, microbodies, and mitochondria) and two biotin-containing enzymes, geranoyl-CoA carboxylase and 3-methylcrotonyl-CoA carboxylase.     

Modulation of p27(Kip1) levels by the cyclin encoded by Kaposi's sarcoma-associated herpesvirus

DNA tumour viruses have evolved a number of mechanisms by which they deregulate normal cellular growth control. We have recently described the properties of a cyclin encoded by human herpesvirus 8 (also known as Kaposi's sarcoma-associated herpesvirus) which is able to resist the actions of p16(Ink4a), p21(Cip1) and p27(Kip1) cdk inhibitors. Here we investigate the mechanism involved in the subversion of a G1 blockade imposed by overexpression of p27(Kip1). We demonstrate that binding of K cyclin to cdk6 expands the substrate repertoire of this cdk to include a number of substrates phosphorylated by cyclin-cdk2 complexes but not cyclin D1-cdk6. Included amongst these substrates is p27(Kip1) which is phosphorylated on Thr187. Expression of K cyclin in mammalian cells leads to p27(Kip1) downregulation, this being consistent with previous studies indicating that phosphorylation of p27(Kip1) on Thr187 triggers its downregulation. K cyclin expression is not able to prevent a G1 arrest imposed by p27(Kip1) in which Thr187 is mutated to non-phosphorylatable Ala. These results imply that K cyclin is able to bypass a p27(Kip1)-imposed G1 arrest by facilitating phosphorylation and downregulation of p27(Kip1) to enable activation of endogenous cyclin-cdk2 complexes. The extension of the substrate repertoire of cdk6 by K cyclin is likely to contribute to the deregulation of cellular growth by this herpesvirus-encoded cyclin.     

Pressure retarded osmosis: From the vision of Sidney Loeb to the first prototype installation — Review

The energy released from the mixing of freshwater with saltwater is a source of renewable energy that can be harvested using pressure retarded osmosis (PRO). In PRO, water from a low salinity solution permeates through a membrane into a pressurized, high salinity solution; power is obtained by depressurizing the permeate through a hydroturbine. The combination of increased interest in renewable and sustainable sources of power production and recent progress in membrane science has led to a spike in PRO interest in the last decade. This interest culminated in the first prototype installation of PRO which opened in Norway in late 2009. Although many investigators would suggest there is still lack of theoretical and experimental investigations to ensure the success of scaled-up PRO, the Norway installation has evoked several specialized and main-stream press news articles. Whether the installation and the press it has received will also boost competitive commercialization of membranes and modules for PRO applications remains to be seen. This state-of-the-art review paper tells the unusual journey of PRO, from the pioneering days in the middle of the 20th century to the first experimental installation.