Neutral Lipase Activity Research Articles

Acid- and neutral lipases involved in endogenous lipolysis in small intestine and heart

Trioleoylglycerol hydrolysis in homogenates of isolated small intestinal villus cells and hearts of rats showed pH optima at 5 and 7. The pH 7 enzyme(s) in contrast to the pH 5 enzyme could be inhibited by 1 μM diethyl p -nitrophenylphosphate. During vascular in vitro perfusions of small intestine and heart this inhibitor severely depressed glycerol release. The lysosomotropic agent methylamine also inhibited endogenous lipolysis in these organs. It is concluded that both acid- and neutral lipases contribute to endogenous lipolysis in small intestine and heart. In heart evidence was obtained that an increase of the lipid depot, by previous trierucate feeding resulted in a relative increase of the contribution of the neutral lipase(s) to overall lipolysis. Extrapolation of this finding to adipose tissue, together with recent literature data, make it very likely that in this tissue neutral lipase activity is far more important than lysosomal enzyme activity in overall endogenous lipid degradation.

Regulation of lipase activities in rat brain in vitro.

Regulation of acid and neutral lipase activities in rat brain was examined in vitro. Both activities were decreased by SDS, CuCl2 and ZnCl2 and by delipidation. The neutral lipase activity was also markedly reduced by N-ethylmaleimide and PbCl2. The activity of delipidated preparation was increased by addition of phosphatidyl choline at both pH 5.5 and 7.5 and by phosphatidyl serine at acidic pH value. Pretreatments of the enzyme preparation with phospholipase A and trypsin reduced the lipase activities at both pH values. It is suggested that phospholipids play an important role on lipase activity in brain.

Characterization of triglyceride lipase activities in rat heart

Triglyceride lipase activity was determined in particulate and soluble fractions from rat heart homogenates. Lipoprotein lipase activity was identified in the 100 000 × g supernatant fraction by the following in vitro criteria: stimulation of lipase activity by serum; maximal activity at alkaline pH (pH 8.2 to 8.4); and inhibition of lipase activity with NaCl. Triglyceride lipase activity was also determined under conditions in which the contribution of lipoprotein lipase to the assay was minimal. Particulate fractions (17 000 × g and 100 000 × g pellets) exhibited both an acid (pH 4.5 to 5) and a neutral (pH 7.5 to 8) pH optimum; the soluble (100 000 × g supernatant) fraction was characterized as having a single pH optimum of 7.5. The acid pH optimum for triglyceride lipase in the particulate fractions suggests that this activity originated in cardiac lysosomes, however the distribution of lipase activity determined at pH 5 did not correlate well with the lysosomal marker enzyme, N-acetyl-β-glucosaminidase. Chloroquine inhibited the acid triglyceride lipase (half maximal inhibition at 3 to 4 m m). In contrast, low concentrations (2 to 5 m m) of chloroquine stimulated lipase activity determined at pH 7.5; higher concentrations then inhibited enzyme activity. Similar results were obtained with NaCl; acid lipase activity was inhibited by all concentrations of NaCl whereas neutral lipase activity was first stimulated (25 to 150 m m NaCl) and then inhibited (200 to 500 m m NaCl). The addition of MgCl 2 (2 to 25 m m) resulted in an inhibition of lipase activity determined at pH 5 and a stimulation of activity determined at pH 7.5. Preincubation of the various rat heart fractions with ATP, cyclic AMP and protein kinase resulted in no change in lipase activity determined at either pH 5 or pH 7.5.

Acid and neutral lipases of cultured adipocytes of infants and children.

In order to determine whether the mobilization of intracellular triglycerides observed in cultured human adipocytes is associated with changes in the activities of acid and neutral lipases, the activities of both enzymes were measured weekly on cultured adipocytes for several months. The activity of acid lipase was initially very low, but rose to levels 40 times the original activity within 3 months. The activity of neutral lipase decreased rapidly within the first 2-4 weeks and remained at approximately 25% of original levels thereafter.

Neutral and acid lipase of mouse 3T3 fibroblasts with increased adipose conversion

In the resting state, 3T3-L1 fibroblasts become adipose converted and increase their fatty acid and triglyceride synthetase. We have found that they contain four times the neutral lipase activity and 1.5 times the acid lipase activity of logarithmically dividing cells. The activities of lysosomal acid β-galactosidase and N-acetyl- β-D-glucosaminidase were the same in the adipose converted and logarithmically dividing cells. The data suggest a possible relation between the increased neutral lipase activity in 3T3-L1 cells and their adipose conversion and demonstrates that the adipose converted 3T3-L1 fibroblasts, unlike true adipose cells, contain high levels of lysosomal acid hydrolases.

Effects of insulin on lipoprotein lipase activity in the rat heart and adipose tissue.

Effects of insulin on lipoprotein lipase activity in the rat heart and adipose tissue.

Intracellular distribution of lipolytic activity in the female gametophyte of germinating Douglas fir seeds

Acid (pH 5.2) and neutral (pH 7.1) lipase activity was studied in order to localize the sites of lipolysis in cellular fractions of catabolic organ of Douglas fir seed. Cellular particles were separated by differential centrifugation of the tissue homogenate and identified by electron microscopy. Emulsified native neutral lipids were provided as a substrate to protein body, mitochondrial, microsomal and soluble fractions, and endogenous lipids were used as a substrate for light and heavy fat body fractions. Little difference was observed in average specific activity of the two enzyme systems in dry seeds, but acid lipase activity increased sevenfold and neutral lipase activity fourfold during germination. Highest specific activity of both enzyme systems was found to be associated with the heavy fat bodies and the soluble fraction. Heavy fat bodies contained an ample quantity of endogenous substrate while the soluble fraction consisted of little substrate. Experimental data indicated that the soluble fraction was the source of lipases, and the heavy fat bodies were the site of in situ lipolysis.