We tested the ability of human liver microsomes (HLMs) and recombinant human cytochrome P450 (CYP or P450) isoforms to catalyze the N-demethylation of nirvanol-free (S)-mephenytoin [(S)-MP] in vitro. In mixed HLMs, the kinetics of (S)-MP N-demethylation suggested two contributing activities. A high-affinity/low-capacity component exhibited a KM of 174.1 microM and a Vmax of 170.5 pmol/mg protei...

The effects of different 1,2-diacyl-sn-glycerols on the kinetic properties of CDP-choline:1,2-diacylglycerol cholinephosphotransferase (EC 2.7.8.2) from mouse liver microsomes have been studied. Initial-velocity experiments were carried out with various concentrations of several species of diacylglycerol at different fixed concentrations of CDP-choline. Kinetic analysis of these data showed a f...

Comparison of the farnesyl diphosphate (FPP) synthase amino acid sequences from four species with amino acid sequences from the related enzymes hexaprenyl diphosphate synthase and geranylgeranyl diphosphate synthase show the presence of two aspartate rich highly conserved domains. The aspartate motif ((I, L, or V)XDDXXD) of the second of those domains has homology with at least 9 prenyl transfe...

The substrate specificity of the catalytic subunit of rabbit skeletal muscle 3': 5'-cyclic AMP-dependent protein kinase (EC 2.7.1.37; ATP: protein phosphotransferase) has been studied using the synthetic peptide Arg-Gly-Tyr-Ser-Leu-Gly corresponding to the sequence around serine 24, a phosphorylation site in reduced, carboxymethylated, maleylated (RCMM) chicken egg white lysozyme. This peptide ...

Rates of peroxisomal beta-oxidation were measured as fatty acyl-CoA-dependent NAD+ reduction, by using solubilized peroxisomal fractions isolated from livers of rats treated with clofibrate. Medium- to long-chain saturated fatty acyl-CoA esters as well as long-chain polyunsaturated fatty acyl-CoA esters were used. Peroxisomal beta-oxidation shows optimal specificity towards long-chain polyunsat...

Sodium-proton antiporter activity can be modulated through changes Vmax and/or intracellular proton sensitivity of the antiporter. To characterize a parathyroid hormone (PTH)-induced decrease in antiporter activity in a continuous renal cell line (opossum kidney cells), the extracellular sodium and intracellular proton dependence of amiloride-inhibitable 22Na uptake was studied. The Km for extr...

The production of platelet-activating factor (PAF) by inflammatory cells is regulated by lyso-PAF acetyltransferase, and the activity of this enzyme is increased in neutrophils of stable asthmatic patients. The aim of this investigation was to determine whether acetyltransferase activity is further upregulated in asthmatic patients experiencing acute symptoms. A radioenzymatic assay was used to...

The effect of bovine serum albumin (BSA) on human liver metabolism, in vitro, of 14C-phenytoin (PHT) was studied. Michaelis Menten parameters were determined for the conversion of PHT to p-hydroxy phenytoin in seven different microsomal preparations with the addition of 0, 2, and 4% BSA. The unbound Km (Kmu) values were 30.8 +/- 18.6, 1.57 +/- 0.21 and 1.50 +/- 0.17 microM (mean +/- S.D.), resp...