Rat Liver Microsomal Activity Research Articles

Inhibition of Enzyme Activities by Free Fatty Acids

The inhibition of several enzyme activities by free fatty acids has been examined. The inhibition of rat liver microsomal linolenate-activating enzyme activity by linolenate was found to be due to the inactivation of enzyme by substrate fatty acid. Stearoyl coenzyme A was also found to inhibit linolenate-activating enzyme. Likewise, microsomal glucose 6-phosphatase was inhibited by oleate; the extent of inhibition by oleate was related to the relative concentration of microsomal material. Citrate synthase from pig heart was inhibited by linoleate and glucose 6-phosphate dehydrogenase of yeast was inhibited by oleate. The inhibition of glucose 6-phosphate dehydrogenase was time-dependent and the presence of glucose 6-phosphate gave considerable protection against inactivation. The marked similarity in the observed inhibition of diverse enzymes by long chain unsaturated fatty acids to that of reported inhibitions by fatty acyl-CoA esters suggests that inhibitory effects are due to detergent properties of these inhibitors. In view of these and other considerations it is suggested that the extrapolation of observed inhibitions in vitro of enzyme activities by free fatty acids to regulation of metabolism in vivo must be made with caution.

Increase of NAD-glycohydrolase activity of rat-liver microsomes by starvation

Increase of NAD-glycohydrolase activity of rat-liver microsomes by starvation

Ribonucleic acid degrading activity of rat liver microsomes following partial hepatectomy.

THE mechanism of cellular proliferation following tissue injury is unclear. Cytochemical and biochemical investigations have shown that the onset of mitotic activity in injured tissues is preceded by an early regressive phase when ribonucleoprotein and RNA are affected1. Clear structural changes in the ergastoplasm of rat liver have been observed in the first hours after partial hepatectomy2,3. These changes are accompanied by a sharp decrease in the ability of RNA to bind basic dyes3. There are also some data indicating that the injury induced changes in RNA may be due to an activation of latent RNA degrading enzymes1,4. Ribosomes from different sources are known to contain a latent RNase which can be activated under the influence of different agents5–7. Another RNA degrading enzyme, a phosphodiesterase, was also found in the microsomal fraction8.

Phospholipase activity in rat-liver microsomes studied by the use of endogenous substrates

1. 1. Degradation of endogenous phospholipids in liver microsomes in vitro has been studied using microsomes from rats injected with the phospholipid precursors [1,2- 14C]ethanolamine, l-[ Me- 14C]methionine and [ 32P]orthophosphate. 2. 2. Calcium and magnesium ions greatly stimulated the breakdown of endogenous phosphatidylethanolamine, but had little influence on the degradation of lecithin. 3. 3. The main reaction products in the degradation of phosphatidylethanolamine have been shown to be glycerylphosphorylethanolamine and free fatty acids, while the main reaction product in the breakdown of lecithin was free choline. 4. 4. The degradation of phosphatidylethanolamine is most probably due to two enzymes: a phospholipase A (phosphatide acyl-hydrolase, EC 3.1.1.4) and a lysophospholipase (lysolecithin acyl-hydrolase, EC 3.1.1.5). 5. 5. Some of the properties of the phosphatidylethanolamine-hydrolyzing enzymic system have been determined and the findings are discussed in relation to previous studies of phospholipid-hydrolyzing enzymes in rat liver.

Alloxan diabetes and insulin effects on a mino acid-incorporating activity of rat liver microsomes.

Summary(1) Liver microsomes from severely diabetic rats incorporate leucine-1-C14 into protein at a lower rate than microsomes from diabetic control rats maintained on insulin. The former have also a lower phospholipid-P and a higher RNA content per unit of protein-N. (2) Microsomes from normal rats incorporate amino acids at a higher rate after injection of insulin. (3) These changes occurred specifically in microsomes; no difference was found with respect to ability of soluble fractions to activate microsomal incorporation. Insulin was without effect upon the microsomal system in vitro.Addendum: Korner(17) found amino acid incorporating capacity of liver microsomes from a different type of diabetic rat to be defective.

Studies on the function of intracellular ribonucleases. III. The relationship of the ribonuclease activity of rat liver microsomes to their biological activity.

Attempts have been made to prepare rat liver microsomes and ribosomes free of RNase activity. Washing of microsomes with a large number of reagents, as well as preparation of microsomes by homogenizing the liver in the presence of a variety of reagents chosen to remove or inhibit RNase activity, failed to abolish completely the enzyme activity. However, when rat liver was homogenized in the presence of optimal concentrations of ATP the microsomes subsequently obtained showed no RNase activity. The composition of such microsomes was compared to controls prepared without the use of ATP. Preparation of microsomes with the use of ATP apparently repressed but did not remove the RNase activity for, when such microsomes were treated with 1 per cent deoxycholate to obtain ribosomes, the latter exhibited normal RNase activity. A possible explanation for these results based on several experiments is given. The incorporation of C(14) of L-leucine-C(14) into control and ATP-treated microsomes was measured. Repression of RNase activity by use of ATP or with RNase inhibitor, significantly reduced the incorporation. As a result of these and other experiments it is tentatively concluded that an alkaline RNase is a normal constituent of rat liver ribosomes and plays a role in the biological activity of these particles.

Eine Methode zur direkten Messung der O-Demethylierung in Lebermikrosomen und ihre Anwendung auf die Mikrosomenhemmwirkung von SKF 525-A

1. A method is described for spectrophotometric determination of the enzymatic activity of rat liver microsomes using the O-demethylation of o-nitroanisole. The latter is demethylated to o-nitrophenol, which can easily and quickly be measured.