Oxidation of apolipoprotein(a) inhibits kringle-associated lysine binding: the loss of intrinsic protein fluorescence suggests a role for tryptophan residues in the lysine binding site

Lipoprotein(a) [Lp(a)] is a low-density lipoprotein complex consisting of apolipoprotein(a) [apo(a)] disulfide-linked to apolipoprotein B-100. Lp(a) has been implicated in atherogenesis and thrombosis through the lysine binding site (LBS) affinity of its kringle domains. We have examined the oxidative effect of 2,2'-azobis-(amidinopropane) HCl (AAPH), a mild hydrophilic free radical initiator, upon the ability of Lp(a) and recombinant apo(a), r-apo(a), to bind through their LBS domains. AAPH treatment caused a time-dependent decrease in the number of functional Lp(a) or r-apo(a) molecules capable of binding to fibrin or lysine-Sepharose and in the intrinsic protein fluorescence of both Lp(a) and r-apo(a). The presence of a lysine analogue during the reaction prevented the loss of lysine binding and provided a partial protection from the loss of tryptophan fluorescence. The partial protection of fluorescence by lysine analogues was observed in other kringle-containing proteins, but not in proteins lacking kringles. No significant aggregation, fragmentation, or change in conformation of Lp(a) or r-apo(a) was observed as assessed by native or SDS-PAGE, light scattering, retention of antigenicity, and protein fluorescence emission spectra. Our results suggest that AAPH destroys amino acids in the kringles of apo(a) that are essential for lysine binding, including one or more tryptophan residues. The present study, therefore, raises the possibility that the biological roles of Lp(a) may be mediated by its state of oxidation, especially in light of our previous study showing that the reductive properties of sulfhydryl-containing compounds increase the LBS affinity of Lp(a) for fibrin.     

Label-free electrochemical monitoring of concentration enrichment during bipolar electrode focusing

We show that a label-free electrochemical method can be used to monitor the position of an enriched analyte band during bipolar electrode focusing in a microfluidic device. The method relies on formation of a depleted buffer cation region, which is responsible for concentration enrichment of the charged analyte. However, this depletion region also leads to an increase in the local electric field in the solution near a bipolar electrode (BPE), and this in turn results in enhanced faradaic reactions (oxidation and reduction of water) at the BPE. Therefore, it is possible to detect the presence of the concentrated analyte band by measuring the current passing through the BPE used for concentration enrichment, or the concentrated band can be detected at a secondary BPE dedicated to that purpose. Both experiments and simulations are presented that fully elucidate the underlying phenomenon responsible for these observations.     

ORIGIN AND ESTIMATION OF THE GUSHING POTENTIAL OF ISOMERIZED HOP EXTRACTS

Two types of gushing promoter have been isolated from isomerized hop extracts. One type is a humulinicacid dehydration product which occurs rarely insuch extracts. The other type of gushing promoter consists of a mixture of oxidation products of hop resins, and is present in all the isomerized extracts examined. The higher the concentration of these oxidation products in a beer the greater is its tendency to gush. α-Acids and cohulupone have been shown to be effective gushing inhibitors. The gushing potential of an isomerized extract appears to be determined mainly by the relative proportions of oxidized materials and unchanged α-acid, present as contaminants. A method for determining the gushing susceptibility of a beer is described.     

THE LOSSES OF BITTER SUBSTANCES DURING FERMENTATION

Almost all of the bitter substances which are lost during pilot-scale brewery fermentations using yeast N.C.Y.C. 240 can be recovered unchanged. The largest losses of bitter substances are associated with the dirty head formed during the first 18 hours of a fermentation. Hop utilization can be improved by folding this dirty head back into the fermenting wort. This process is most effective when carried out after the ethanol concentration of the wort has reached about 1%, but before the bitter substances have had the opportunity to undergo extensive oxidative degradation. Losses of bitter substances are lower when 25% of a malt grist is replaced by wheat flour. There is no consistent relationship between losses of bitter substances and either the assimilable or total nitrogen of wort. With increase in wort O.G. there is increasing loss of bitter substances, such losses being principally associated with the dirty head.     

EFFECT OF STORAGE ON HOP EXTRACTS

Representative commercial hop extracts suffered no appreciable loss either of α- or β-acids or of bittering value when kept for 2 to 21 months in closed containers. Though there was loss of α- and β-acids on prolonged exposure of the extracts to air, it did not lead to a corresponding loss of bittering value. Of a range of commercial isomerized extracts, most proved satsifactorily stable on storage. However, when large losses of iso-α-acids did occur they were accompanied by corresponding reductions in bittering value. With reference to bittering compounds, there appeared to be no significant differences in the storage stability of beers bittered using hops or extracts of various types.     

MEMS variable‐capacitor phase shifters part II: Reflection‐type phase shifters

A novel design procedure for reflection‐type phase shifters using capacitive devices is developed. Using this approach, a phase shifter for operation at 26.5 GHz is developed using MEMS variable capacitors reported in Part I of this article. A design optimization procedure is discussed. Design of a CPW hybrid at 26.5 GHz (as needed for this phase shifter) is also discussed. Experimental results validate the design procedure and yield a phase shift of 179.30° at 26.5 GHz. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 415–425, 2003.     

Stiffness changes in unidirectional composites caused by crack systems

This paper is concerned with the development of constitutive equations for fibrous composites which contain a family of longitudinal slit cracks. The general theory in which the crack length is of the same order as the fiber diameter gives rise to a three-phase model. When the fiber diameter is much smaller than the crack length, we obtain the associated two-phase model. Detailed numerical results are given for selected systems.     

HOP EXTRACTS—A REVIEW

The production and use of both hop extracts and isomerized hop extracts is reviewed with particular reference to recent advances in hop extract technology.     

THE CHEMISTRY OF HOP CONSTITUENTS XXX. SYNTHETIC ISO-α-ACIDS

(±)-Isocohumulone and (±)-iso-adhumulone have been synthesized in low overall yield by a route similar to that used to synthesize (±)-isohumulone.