Gene/Protein Disease Symptom Drug Enzyme Compound
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Biopsies of the gluteus medius muscle were taken at three different depths from 36 endurance horses aged 8.42 +/- 2.85 years and of both sexes. Twenty of the horses were considered to be excellent performers on the basis of the mean speed of their three fastest records in endurance events over the previous two or three years, whereas 16 were moderate performers. The biopsy samples were analysed for the activities of the enzymes citrate synthase (an indicator of citric acid cycle activity), 3-OH-acyl-CoA-dehydrogenase (an indicator of lipid oxidation) and lactate dehydrogenase (an indicator of anaerobic metabolism). The 20 excellent performers had higher activities of citrate synthase (P < 0.001) and 3-OH-acyl-CoA-dehydrogenase (P < 0.02) than the 16 moderate performers. The activities of citrate synthase and 3-OH-acyl-CoA-dehydrogenase increased by 65 per cent and 75 per cent, respectively, and the activity of lactate dehydrogenase decreased by 23 per cent in the samples taken at successively greater depths. There was a strong linear relationship between the ratios of the activities of lactate dehydrogenase/citrate synthase and lactate dehydrogenase/3-OH-acyl-CoA-dehydrogenase and the depth from which the samples were taken for both performance groups (P < 0.001). The intercepts of the regression lines were higher in the moderate than in the excellent performers (P < 0.001 and P < 0.01 for the two ratios), showing that the endurance horses with the better performance record had a greater aerobic capacity and a relatively lower anaerobic capacity in the gluteus medius muscle than the horses with a poorer record.
Vet Rec 1995 Aug 19
PMID:Activities of selected aerobic and anaerobic enzymes in the gluteus medius muscle of endurance horses with different performance records. 856 Jul 24

Polyketide biosynthesis is catalyzed by polyketide synthase (PKS) and three types of bacterial PKS are known to date. Feeding experiments with isotope-labeled precursors established the polyketide origin of the macrotetrolides, but the labeling pattern cannot be rationalized according to the established PKS paradigm. Genetic analysis of the macrotetrolide biosynthesis unveiled an unprecedented organization for a polyketide gene cluster that features five genes encoding discrete ketoacyl synthase (KS) and four genes encoding discrete ketoreductase (KR) but lacking an acyl carrier protein (ACP). Macrotetrolide biosynthesis is proposed to involve a novel type II PKS that acts directly on acyl CoA substrates, functions noniteratively, and catalyzes both C-C and C-O bond formation. These findings demonstrate once again Nature's versatility in making complex molecules and suggests new strategies for PKS engineering to further expand the scope and diversity of polyketide library. They also should serve as an inspiration in searching for PKS with novel chemistry for combinatorial biosynthesis.
Chem Rec 2002
PMID:Macrotetrolide biosynthesis: a novel type II polyketide synthase. 1246 50

DHHC proteins catalyze the reversible S-acylation of proteins at cysteine residues, a modification important for regulating protein localization, stability, and activity. However, little is known about the kinetic mechanism of DHHC proteins. A high-performance liquid chromatography (HPLC), fluorescent peptide-based assay for protein S-acylation activity was developed to characterize mammalian DHHC2 and DHHC3. Time courses and substrate saturation curves allowed the determination of V(max) and K(m) values for both the peptide N-myristoylated-GCG and palmitoyl-coenzyme A. DHHC proteins acylate themselves upon incubation with palmitoyl-CoA, which is hypothesized to reflect a transient acyl enzyme transfer intermediate. Single turnover assays with DHHC2 and DHHC3 demonstrated that a radiolabeled acyl group on the enzyme transferred to the protein substrate, consistent with a two-step ping-pong mechanism. Enzyme autoacylation and acyltransfer to substrate displayed the same acyl-CoA specificities, further supporting a two-step mechanism. Interestingly, DHHC2 efficiently transferred acyl chains 14 carbons and longer, whereas DHHC3 activity was greatly reduced by acyl-CoAs with chain lengths longer than 16 carbons. The rate and extent of autoacylation of DHHC3, as well as the rate of acyl chain transfer to protein substrate, were reduced with stearoyl-CoA when compared with palmitoyl-CoA. This is the first observation of lipid substrate specificity among DHHC proteins and may account for the differential S-acylation of proteins observed in cells.
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PMID:DHHC protein S-acyltransferases use similar ping-pong kinetic mechanisms but display different acyl-CoA specificities. 2224 42