1.1. Unlike the cytosolic proteins, the adipocyte subcellular fractions, in Vitro are capable of incorporating acyl-CoA into phospholipids and glycerides.2.2. The esterification specific activity was found to be higher in plasma membrane and microsomes than in mitochondria.3.3. The selectivity of the lipid products, the sensitivity of the esterification systems to cytosolic proteins as well as the palmityl-CoA/stearyl-CoA esterification ratio (about 2), were found to be the same in the three adipocyte membrane fractions.

The distribution of fatty acid elongation systems in the subcellular fractions of isolated fat cells was studied. These systems were found to be located essentially in the particulate fractions, Acetyl CoA elongation was found to occur predominantly in the mitochondria (2.8 nmoles of acetyl CoA incorporated into fatty acids/mg of proteins per 30 min) while malonyl CoA elongation was predominant in the purified plasma membranes (10 nmoles of malonyl CoA incorporated into fatty acids/mg of proteins per 30 min). The acetyl CoA elongation activity in the mitochondria and the malonyl CoA elongation activity in the purified plasma membranes were found to be 6.4 and 2.4 times higher, respectively, than in the purified microsomes, the next most active fraction. In liver, on the other hand, greater malonyl CoA elongation activity was found in microsomes than in plasma membranes.

The influence of the mode of preparation upon some of the characteristics of white adipose tissue plasma membranes and microsomes has been reported. Plasma membrane fractions prepared from mitochondrial pellet were shown to have higher specific activities of (Mg2+ + Na+ + K+)-ATPase than plasma membranes originating in crude microsomes. Isolation of fat cells by collagenase treatment was found to result in a decrease in specific activity of the plasma membrane enzymes; in plasma membranes prepared from isolated fat cells, the specific activity values obtained for (Mg2+ + Na+ +k+)-ATPase and 5'-nucleotidase were only 42% and 6.3% respectively of those obtained in plasma membranes prepared from whole adipose tissue. Purification of whole adipose tissue crude microsomes by hypotonic treatment caused extensive solubilization of the endoplasmic reticulum marker enzymes, NADH oxidase and NADPH cytochrome c reductase. The lability of endoplasmic reticulum marker enzymes, however, was found to be greatly diminished in the preparations from isolated fat cells. The possibility that NADH oxidase and NADPH cytochrome c reductase activities found in the plasma membranes are microsomal enzymes adsorbed by the plasma membranes is discussed. The peptide patterns as well as the NADH oxidase and NADPH cytochrome c reductase activity patterns of plasma membranes and purified microsomes were compared by means of sodium dodecyl sulfate or Triton X-100 polyacrylamide gel electrophoresis.

Triglyceride and monoglyceride lipase activities were compared in different preparations from rat adipose tissue or isolated adipocytes: fat‐free homogenate, 105000 ×g fat‐free infranatant (soluble fraction) and 105000 ×g sediment (particulate fraction) were assayed. The ratio of monoolein to triolein cleavage was 6.8 in whole homogenate and 1.9 and 20 in particulate and soluble fractions, respectively. Lipoprotein lipase activity of these enzyme preparations was not measurable under the experimental conditions used. Since specific activities especially of triglyceride lipase(s) were low, other substrates were tested to increase the sensitivity. Among them 2‐naphthol laurate was found to be hydrolyzed by the whole homogenate at a rate about 50 times higher than triolein. 2‐Naphthol laurate was readily hydrolyzed by lipases in all preparations studied. Dioxane and ethylene glycol, the typical inhibitors of monoglyceride lipase activity strongly inhibited its cleavage in the soluble fraction whereas the typical inhibitors of triglyceride lipase activity (Triton ×‐100, lanthanum nitrate, 2‐propanol) were effective in inhibiting 2‐naphthol laurate cleavage particularly in 105000 ×g sediment. Heat inactivation, pH optima and starch‐block electrophoresis confirmed the difference between lipases in particulate and soluble fractions. Whereas in the soluble fraction these criteria did not reveal further heterogeneity, the particulate fraction was apparently heterogenous and exhibited two pH optima at 6.5 and 8, a non‐linear rate of heat inactivation with time and two electrophoretic fractions, thus suggesting the presence of two distinct triglyceride lipases. The monoglyceride lipase character of the soluble lipase is supported by the kinetic evidence of competition between monoolein and 2‐naphthol laurate. The particulate lipases, on the other hand, exhibited competitive inhibition of 2‐naphthol laurate cleavage by triolein, which supports their triglyceride lipase character. 2‐Naphthol laurate might be thus a valuable tool in the study of both monoglyceride and triglyceride lipase activities in adipose tissue. The possibility of high dilution of enzyme preparation excludes the interference of endogenous substrate, the preparation of a stable substrate emulsion is easy and the estimation of the first product of the reaction is rapid and simple.

FEBS LettersVolume 37, Issue 2 p. 264-268 Full-length articleFree Access Stimulation of adipose tissue triglyceride lipase activity after in vivo administration of dibutyryl cyclic AMP or norepinephrine First published: December 01, 1973 https://doi.org/10.1016/0014-5793(73)80475-2Citations: 3AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume37, Issue2December 01, 1973Pages 264-268 ReferencesRelatedInformation

In der Aortenwand von Ratten, Meerschweinchen, Kaninchen und Schweinen wird eine hormonempfindliche Lipase beschrieben, die in vitro durch Katecholamine, ACTH und Glucagon beeinflusst wird. Glucagonfreies Insulin wies eine deutliche lipolytische Wirkung auf und unterschied sich dadurch von der Wirkung im Fettgewebe.

Die in vitro-Wirkung des Insulins (Konzentrationsbereich von 50–100 000µU/ml des Inkubationsmediums) auf die esterolytische Aktivität der Fettgewebe, Homogenate von Myokard, Lunge und Muskel wurde bei Ratten beschrieben. Es ergibt sich eine von der Enzym-Synthese unabhängige schnelle Insulinwirkung.