Ubihydroquinone: cytochrome (cyt) c oxidoreductase, or cyt bc1, is a widespread, membrane integral enzyme that plays a crucial role during photosynthesis and respiration. It is one of the major contributors of the electrochemical proton gradient, which is subsequently used for ATP synthesis. The simplest form of the cyt bc1 is found in bacteria, and it contains only the three ubiquitously conserved catalytic subunits: the FeS protein, cyt b and cyt c1. Here we present a preliminary X-ray structure of Rhodobacter capsulatus cyt bc1 at 3.8 Angstrom, and compare it to the available structures of its homologues from mitochondria and chloroplast. Using the bacterial enzyme structure, we highlight the structural similarities and differences that are found among the three catalytic subunits between the the different members of this family of enzymes. In addition, we discuss the locations of currently known critical mutations, and their implications in terms of the cyt bc1 catalysis.

We have investigated the valley splitting of two-dimensional electrons in high-quality Si Si1-x Gex heterostructures under tilted magnetic fields. For all the samples in our study, the valley splitting at filling factor ν=3 (Δ3) is significantly different before and after the coincidence angle, at which energy levels cross at the Fermi level. On both sides of the coincidence, a linear dependence of Δ3 on the electron density was observed, while the slope of these two configurations differs by more than a factor of 2. We argue that screening of the Coulomb interaction from the low-lying filled levels, which also explains the observed spin-dependent resistivity, is responsible for the large difference of Δ3 before and after the coincidence. © 2006 The American Physical Society.

The impact of common variants in the apolipoprotein gene cluster (APOC3-A4-A5) on prospective CHD risk was examined in healthy UK men. Of the 2808 men followed over nine years, 187 had a clinically defined CHD event. Examination of 9 single nucleotide polymorphisms (SNPs) in this group revealed that homozygotes for APOA4 S347 had significantly increased risk of CHD [Hazard ratio (HR) of 2.07 (95%CI 1.04-4.12)] while men homozygous for APOC3 1100T were protected (HR 0.28 (95%CI 0.09-0.87)). In stepwise multiple regression analysis, after entering all the variants and adjusting for established risk factors APOA4 T347S alone remained in the model. Using nine-SNP haplotype analysis, highest risk-estimate haplotypes carried APOA4 S347 and rare alleles of the two flanking intergenic markers. The protective effect of APOC31100T could be explained by negative linkage disequilibrium with these alleles. To determine the association of APOA4 T347S with apoAIVlevels, the relationship was examined in over 1600 healthy young European men and women. S347 homozygotes had significantly lower apoAIV plasma levels (13.48 + 0.6mg/dl) compared to carriers of the T347 allele (14.85 + 0.12 mg/dl) (p=0.025). These results demonstrate that genetic variation in and around APOA4, independent of effects of TG, is associated with risk of CHD and apoAIV levels, supporting an anti-atherogenic role for apoAIV.