Some studies on the metabolism of phospholipids in plasma membranes from rat liver

1. 1. Rat liver plasma membranes were isolated by rate-isopycnic zonal centrifugation. A method is described for the size 14 zonal rotor. The isolated membranes had an isopycnic banding density of 41.2% sucrose (w/w). On the basis of studies with eleven marker enzymes and electron microscopy, at least 90% of the fraction consisted of plasma membranes. The electron micrographs showed a predominantly vesicular appearance with few junctional complexes. 2. 2. Plasma membranes exhibited virtually no CDP-choline: 1, 2-diacyl-sn-glycerol cholinephosphotransferase activity and thus appear incapable of significant in vitro synthesis of phosphatidylcholine by the cytidine nucleotide pathway. 3. 3. Phosphatidylglycerol was the major product of sn-glycerol-3-phosphate esterification by plasma membranes in the presence of CDP-diglyceride at pH 7.5. The product was identified by thin-layer chromatography using pure phosphatidylglycerol as a reference compound, and by paper chromatography of the products obtained by hydrolysis with phospholipase D. 4. 4. Incubation of plasma membranes with labeled exogenous phospholipids in the presence of Ca2+ resulted in the formation of fatty acids and monoacylphosphoglycerides. Analyses of the reaction products indicated that the phospholipase A mainly attacks the 2-position of the phosphoglyceride molecule. Plasma membrane phospholipase A also acted on labeled endogenous phosphatidylethanolamine in the presence of Ca2+. 5. 5. A partial characterization of the phospholipase indicated that it required Ca2+ for optimal activity, was insensitive to N-ethylmaleimide and deoxycholate, and was relatively heat stable. Its pH optimum was 8.0. The following was the preferred order of hydrolysis: phosphatidylethanolamine > phosphatidylglycerol > > > phosphatidylcholine. 6. 6. Lysophospholipase was not detected in rat liver plasma membranes under conditions in which maximal activity of this enzyme was observed in rat liver 100 000 × g supernatant

The role of oxidative stress in small ruminants' health and production O papel do estresse oxidativo na saúde e produção de pequenos ruminantes

This paper examines the role that oxidative stress plays in small ruminant medicine. We will examine how redox homeostasis is involved in some physiological functions and we will discuss the implications of the impairment of oxidative status on small ruminant health and production.<br>Este artigo analisa o papel do estresse oxidativo sobre a medicina de pequenos ruminantes. Será examinado o envolvimento da homeostase redox em algumas funções fisiológicas e discutidas as implicações do comprometimento do estado oxidativo sobre a saúde ea produção de pequenos ruminantes