Peroxynitrite (ONOO-) toxicity is associated with protein oxidation and/or tyrosine nitration, usually resulting in inhibition of enzyme activity. We examined the effect of ONOO- on the activity of purified rat liver microsomal glutathione S-transferase (GST) and found that the activity of reduced glutathione (GSH)-free enzyme was increased 4- to 5-fold by 2 mM ONOO-; only 15% of this increased...

The aim of the present study was to characterize the acyl-coenzyme A: cholesterol acyltransferase (ACAT) activity in human liver microsomes. Liver biopsies were obtained from patients undergoing elective cholecystectomy under highly standardized conditions. In 34 patients the enzyme activity of the microsomal fraction averaged 6.6 +/- 0.7 (mean +/- SEM) pmol.min-1.mg protein-1 in the absence of...

1. Tyrosine aminotransferase from guinea-pig liver is inactivated at neutral pH by a factor localized in the microsomal fraction. The inactivation, independent of exogenous L-cysteine, is rapidly reversed by addition of dithiothreitol. 2. The effects of physiological reducing agents on the enzyme inactivation were investigated. L-Cysteine and L-cysteamine enhance the inactivation rate of the en...

The purpose of these studies was to determine the properties of the membrane-bound cytidylyltransferase in adult lung and to assess the relationship between the microsomal enzyme and the two forms of cytidylyltransferase in cytosol. Microsomes, isolated by glycerol density centrifugation, contained significantly less cytidylyltransferase than microsomes isolated by differential centrifugation (...

A 25 kDa subunit of glutathione S-transferase (GST) from sheep liver microsomes (microsomal GSTA1-1) with a significant selenium-independent glutathione peroxidase activity has been isolated and characterized. Several analytical criteria, including EDTA stripping, protease protection assay and extraction with alkaline Na(2)CO(3), indicate that the microsomal GSTA1-1 is associated with the inner...

Fatty acid synthesis is traditionally viewed as being confined to the cytosolic cellular fraction, although a substantial body of data indicates that both microsomes and mitochondria are capable of initiating fatty acid synthesis and may contain acetyl-CoA carboxylase [acetyl-CoA:carbon-doxide ligase (ADP-forming), EC 6.4.1.2], fatty acid synthetase, and ATP-citrate lyase [ATP citrate (pro-3S)-...

Rat liver microsomes contain an enzyme that catalyzes the isomerization of the nuclear double bond of steroids from the 8(9) position to the 7(8) position. The enzyme is most active with zymosterol, 5alpha-cholesta-8,24-dien-3beta-ol, which is a precursor of cholesterol. Properties of the microsomal isomerase have now been studied, and preliminary data are reported on both regulation of enzymic...