INVESTIGATION OF MICROSOMAL OXYGENASES OF BIOSYNTHETIC PROCESSES - STEARYL-COA DESATURASE OF ADIPOSE-TISSUE AND LIVER

  • 1 January 1976
    • journal article
    • research article
    • Vol. 251  (23) , 7468-7473
Abstract
Porcine and rat microsomal stearyl-CoA desaturases require reduced pyridine nucleotide and O2, are cyanide sensitive, and are insensitive to CO. The Km for stearyl-CoA is somewhat larger for liver than for the adipose desaturases, but, in general, assay conditions are quite similar. Adipose tissue microsomes contain cytochromes b5 and P-450, as well as the NADH- and NADPH-specific cytochrome reductases. Compared to liver, the specific contents and activities of electron carriers are much lower in adipose tissue, and activities of 4-methyl sterol oxidase of cholesterol biosynthesis, as well as the cytochrome P-450-dependent aminopyrene demethylase and benzypyrene hydroxylase, are negligible in adipose tissue microsomes. Unlike hepatic desaturase, administration of insulin stimulates the adipose 3-fold without affecting either the amounts or activities of microsomal oxidation-reduction proteins; the changes in desaturase activities produced either by altering dietary fat or by fasting and/or fasting followed by refeeding are, in general, both more extensive and more permanent in adipose compared to liver microsomes. The effects produced by 2H substitution both in stearyl-CoA and in the medium (2H2O) are similar with microsomes from both tissues. The rate-determining step of desaturase appears to be similar in both tissues. The primary isotope effect , K2H/K3H, observed with [9,10-3H2]stearyl-CoA is relatively small, 2.88. Since little, if any, primary isotope effect is associated with methyl sterol oxidase, these 2 mixed function oxidases of biosynthetic processes also appear to share this property in common.

This publication has 11 references indexed in Scilit: