Cholesteryl ester and triglyceride hydrolysis by an acid lipase from rabbit aorta

Cholesterol metabolism in the rat lactating mammary gland: the role of cholesteryl ester hydrolase

An acid cholesteryl ester hydrolase activity associated with a fraction containing mitochondria and lysosomes from rat lactating mammary glands was found to have a pH optimum of 5.0. Its sedimentation pattern was closely related to that of the lysosomal enzyme markers acid phosphatase and beta-glucuronidase, suggesting that the activity is associated with the lysosomes. The enzyme was strongly inhibited by Cu2+, but was inhibited little by other divalent metal ions. Acid cholesteryl ester hydrolase activity was almost completely abolished by p-hydroxy-mercuribenzoate, but this effect was reversed in the presence of an equimolar concentration of reduced glutathione (GSH), indicating that the enzyme requires free sulfhydryl groups for activity. These properties are similar to those of acid, lysosomal cholesteryl ester hydrolases found in other tissues. Acid cholesteryl ester hydrolase activity was 8-14 fold higher in mammary tissue from lactating as compared to virgin rats. Neutral cholesteryl ester hydrolase activities associated with the microsomal and cytosolic subcellular fractions were also increased in lactating glands, but to a lesser extent. In addition, a 2-fold increase in the activities of both the acid and microsomal neutral enzymes was seen during the first few days of lactation, while the cytosolic neutral activity remained constant. These results suggest that mammary gland cholesteryl ester hydrolases have a role in the regulation of cholesterol metabolism in mammary cells, and in the provision of cholesterol for secretion into milk.

Acid lipase in rat intestinal mucosa: physiological parameters

Previous studies have shown that up to a half of infused triacylglycerol does not exit the intestine via lymphatics. This suggests the presence of a mucosal lipase which could provide fatty acids for potential transport via the portal vein. The present study describes an acid-active lipase in rat intestinal mucosa. Acid lipase was assayed using a glyceryl tri[14C]oleate emulsion (pH 5.8). Mucosal homogenates were differentially centrifuged to yield cellular organelles and cytosol. Cells were sequentially released from villi using citrate and EDTA. The enzyme was found to be most active in the proximal quarter intestine and in the upper third of villi. Its greatest activity was in the lysosomal fraction. Esophageal diversion demonstrated that lingual lipase was not the precursor of the mucosal acid lipase. Bile salts stimulated activity 3- to 5-fold, but other neutral or anionic detergents were inhibitory. Of the detergents tested, taurocholate at super critical micellar concentrations could restore activity only with SDS. Sepharose 6B chromatography suggested that the enzyme partitioned into an SDS and taurocholate mixed micelle. We conclude that mucosal acid lipase is a distinct, intrinsic enzyme of the intestinal mucosa. It is predominantly lysosomal in origin. The location of its greatest activity in the villus tips of the proximal intestine suggests that it is potentially involved in mucosal triacylglycerol disposal.

Properties of acid and neutral cholesterol ester hydrolases in rat and pigeon aortas

The activity of cholesterol ester hydrolase was measured in subcellular fractions from rat and pigeon aortas using a glycerol-dispersed cholesterol oleate substrate preparation. The specific activity of acid cholesterol ester hydrolase (assayed at pH 5) in adventitia tissue fractions was 40-50 fold greater than in media-intima fractions from rat aorta. Soluble and particulate subcellular fractions from rat aorta (media-intima) were observed to have cholesterol ester hydrolase activity with both an acid (pH 4.5-5) and a neutral (pH 7.5) pH optimum. A comparison of the subcellular distribution of acid cholesterol ester hydrolase with the lysosomal marker enzyme, N-acetylglucosaminidase, suggests that the acid hydrolase activity originated in aortic lysosomes; the neutral cholesterol ester hydrolase was predominantly soluble. Acid and neutral cholesterol ester hydrolases could also be distinguished on the basic of the effects of Mg Cl2 and NaCl on hydrolase activity and on rates of thermal denaturation. Both acid an neutral hydrolases from rat aorta (media-intima) were inhibited by chloroquine (half-maximal at 2-4 mM), and both hydrolases were characterized as having the same apparent affinity for the glycerol-dispersed cholesterol oleate substrate. Acid and neutral cholesterol ester hydrolases were also observed in preparations from pigeon aortas. The specific activity for both acid and neutral hydrolases was higher in atherosclerosis-susceptible White Carneau pigeon aortas in comparison to Show Racer pigeon aortas.

Solubilization and localization of triolein in phosphatidylcholine bilayers: a 13C NMR study

Cosonicated mixtures of egg phosphatidylcholine and small amounts (less than 5% wt/wt) of triolein have been studied by 13C NMR spectroscopy. The 50.3-MHz 13C NMR spectrum of vesicles preparations containing 90% isotopically substituted [1-13C]triolein showed two carbonyl resonances at chemical shift values that indicate hydrogen bonding of H2O molecules with the carbonyl groups. The extent of hydration, estimated from the chemical shift values that indicate hydrogen bonding of H2O molecules with the chemical shift values (173.07 ppm and 172.39 is approximately 50%. The data suggest that the triolein is located in the bilayer with the three carbonyl groups at the aqueous interface. The acyl chains are extended toward the bilayer interior, with a conformation of the glyceryl region such that the primary (alpha) carbonyls are closer to the aqueous medium than is the secondary (beta) carbonyl. Thus, triolein is present in the bilayer in an orientation appropriate for enzymatic hydrolysis, with the second substrate (H2O) in close proximity to the hydrolytic site, and with a conformation that could explain, in part, enzymatic specificity for hydrolysis at the alpha position. Spectra of vesicles containing greater than or equal to 3% triolein showed two additional carbonyl peaks characteristic of pure (neat) triolein. This allowed a determination of the maximum solubility (approximately 2.8%) of surface-oriented triolein in the bilayer phase. Beyond this limit all excess triolein partitions into a separate oil phase.