Separation of bovine brain mono- and diacylglycerol lipases by heparin sepharose affinity chromatography

Endocannabinoid Degradation Enzyme Inhibitors as Potential Antipsychotics: A Medicinal Chemistry Perspective

The endocannabinoid system (ECS) plays a very important role in numerous physiological and pharmacological processes, such as those related to the central nervous system (CNS), including learning, memory, emotional processing, as well pain control, inflammatory and immune response, and as a biomarker in certain psychiatric disorders. Unfortunately, the half-life of the natural ligands responsible for these effects is very short. This perspective describes the potential role of the inhibitors of the enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MGL), which are mainly responsible for the degradation of endogenous ligands in psychic disorders and related pathologies. The examination was carried out considering both the impact that the classical exogenous ligands such as Δ⁹-tetrahydrocannabinol (THC) and (-)-trans-cannabidiol (CBD) have on the ECS and through an analysis focused on the possibility of predicting the potential toxicity of the inhibitors before they are subjected to clinical studies. In particular, cardiotoxicity (hERG liability), probably the worst early adverse reaction studied during clinical studies focused on acute toxicity, was predicted, and some of the most used and robust metrics available were considered to select which of the analyzed compounds could be repositioned as possible oral antipsychotics.

The Endocannabinoid System as a Target for Neuroprotection/Neuroregeneration in Perinatal Hypoxic-Ischemic Brain Injury

The endocannabinoid (EC) system is a complex cell-signaling system that participates in a vast number of biological processes since the prenatal period, including the development of the nervous system, brain plasticity, and circuit repair. This neuromodulatory system is also involved in the response to endogenous and environmental insults, being of special relevance in the prevention and/or treatment of vascular disorders, such as stroke and neuroprotection after neonatal brain injury. Perinatal hypoxia-ischemia leading to neonatal encephalopathy is a devastating condition with no therapeutic approach apart from moderate hypothermia, which is effective only in some cases. This overview, therefore, gives a current description of the main components of the EC system (including cannabinoid receptors, ligands, and related enzymes), to later analyze the EC system as a target for neonatal neuroprotection with a special focus on its neurogenic potential after hypoxic-ischemic brain injury.

2-Arachidonoylglycerol: A signaling lipid with manifold actions in the brain

2-Arachidonoylglycerol (2-AG) is a signaling lipid in the central nervous system that is a key regulator of neurotransmitter release. 2-AG is an endocannabinoid that activates the cannabinoid CB₁ receptor. It is involved in a wide array of (patho)physiological functions, such as emotion, cognition, energy balance, pain sensation and neuroinflammation. In this review, we describe the biosynthetic and metabolic pathways of 2-AG and how chemical and genetic perturbation of these pathways has led to insight in the biological role of this signaling lipid. Finally, we discuss the potential therapeutic benefits of modulating 2-AG levels in the brain.

Endocannabinoid Turnover

In this review, we consider the biosynthetic, hydrolytic, and oxidative metabolism of the endocannabinoids anandamide and 2-arachidonoylglycerol. We describe the enzymes associated with these events and their characterization. We identify the inhibitor profile for these enzymes and the status of therapeutic exploitation, which to date has been limited to clinical trials for fatty acid amide hydrolase inhibitors. To bring the review to a close, we consider whether point block of a single enzyme is likely to be the most successful approach for therapeutic exploitation of the endocannabinoid system.

Disease-specific heteromerization of G-protein-coupled receptors that target drugs of abuse

Drugs of abuse such as morphine or marijuana exert their effects through the activation of G-protein-coupled receptors (GPCRs), the opioid and cannabinoid receptors, respectively. Moreover, interactions between either of these receptors have been shown to be involved in the rewarding effects of drugs of abuse. Recent advances in the field, using a variety of approaches, have demonstrated that many GPCRs, including opioid, cannabinoid, and dopamine receptors, can form associations between different receptor subtypes or with other GPCRs to form heteromeric complexes. The formation of these complexes, in turn, leads to the modulation of the properties of individual protomers. The development of tools that can selectively disrupt GPCR heteromers as well as monoclonal antibodies that can selectively block signaling by specific heteromer pairs has indicated that heteromers involving opioid, cannabinoid, or dopamine receptors may play a role in various disease states. In this review, we describe evidence for opioid, cannabinoid, and dopamine receptor heteromerization and the potential role of GPCR heteromers in pathophysiological conditions.

The diacylglycerol lipases: structure, regulation and roles in and beyond endocannabinoid signalling

The diacylglycerol lipases (DAGLs) hydrolyse diacylglycerol to generate 2-arachidonoylglycerol (2-AG), the most abundant ligand for the CB(1) and CB(2) cannabinoid receptors in the body. DAGL-dependent endocannabinoid signalling regulates axonal growth and guidance during development, and is required for the generation and migration of new neurons in the adult brain. At developed synapses, 2-AG released from postsynaptic terminals acts back on presynaptic CB(1) receptors to inhibit the secretion of both excitatory and inhibitory neurotransmitters, with this DAGL-dependent synaptic plasticity operating throughout the nervous system. Importantly, the DAGLs have functions that do not involve cannabinoid receptors. For example, 2-AG is the precursor of arachidonic acid in a pathway that maintains the level of this essential lipid in the brain and other organs. This pathway also drives the cyclooxygenase-dependent generation of inflammatory prostaglandins in the brain, which has recently been implicated in the degeneration of dopaminergic neurons in Parkinson's disease. Remarkably, we still know very little about the mechanisms that regulate DAGL activity-however, key insights can be gleaned by homology modelling against other α/β hydrolases and from a detailed examination of published proteomic studies and other databases. These identify a regulatory loop with a highly conserved signature motif, as well as phosphorylation and palmitoylation as post-translational mechanisms likely to regulate function.

DAGL-dependent endocannabinoid signalling: roles in axonal pathfinding, synaptic plasticity and adult neurogenesis

Until recently, endocannabinoid (eCB) signalling was largely studied in the context of synaptic plasticity in the postnatal brain in the absence of detailed knowledge of the nature of the enzyme(s) responsible for the synthesis of the eCBs. However, the identification of two diacylglycerol lipases (DAGLα and DAGLβ) responsible for the synthesis of 2-arachidonoylglycerol (2-AG) has increased the understanding of where this eCB is synthesised in relationship to the expression of cannabinoid receptor (CB)1 and CB2. Furthermore, the generation of knockout animals for each enzyme has allowed for the direct testing of their importance for established and emerging eCB functions. Based on this, we now know that DAGLα is enriched in dendritic spines that appose CB1-positive synaptic terminals, and that 2-AG functions as a retrograde signal controlling synaptic strength throughout the nervous system. Consequently, we have built on the principle that expression of eCB components dictates function to identify additional physiological functions of this signalling cassette. A number of studies have now provided support for DAGL-dependent eCB signalling playing important roles in brain development and in cellular plasticity in the adult nervous system. In this article, we will review evidence based on the localisation of the enzymes, as well as from genetic and pharmacological studies, that show DAGL-dependent eCB signalling to play an important role in axonal growth and guidance during development, in retrograde synaptic signalling at mature synapses, and in the control of adult neurogenesis in the hippocampus and subventricular zone.

Bovine brain diacylglycerol lipase: substrate specificity and activation by cyclic AMP-dependent protein kinase

Diacylglycerol lipase (EC 3.1.1.3) was purified from bovine brain microsomes using multiple column chromatographic techniques. The purified enzyme migrates as a single band on SDS-PAGE and has an apparent molecular weight of 27 kDa. Substrate specificity experiments using mixed molecular species of 1,2-diacyl-sn-glycerols indicate that low concentrations of Ca(2+) and Mg(2+) have no direct effect on enzymic activity and 1,2-diacyl-sn-glycerols are the preferred substrate over 1,3-diacyl-sn-glycerols. The enzyme hydrolyzes stearate in preference to palmitate from the sn-1 position of 1,2-diacyl-sn-glycerols. 1-O-Alkyl-2-acyl-sn-glycerols are not a substrate for the purified enzyme. The native enzyme had a V (max) value of 616 nmol/min mg protein. Phosphorylation by cAMP-dependent protein kinase resulted in a threefold increase in catalytic throughput (V (max) = 1,900 nmol/min mg protein). The substrate specificity and catalytic properties of the bovine brain diacylglycerol lipase suggest that diacylglycerol lipase may regulate protein kinase C activity and 2-arachidonoyl-sn-glycerol levels by rapidly altering the intracellular concentration of diacylglycerols.

Cyclooxygenases, lipoxygenases, and epoxygenases in CNS: Their role and involvement in neurological disorders

Three enzyme systems, cyclooxygenases that generate prostaglandins, lipoxygenases that form hydroxy derivatives and leukotrienes, and epoxygenases that give rise to epoxyeicosatrienoic products, metabolize arachidonic acid after its release from neural membrane phospholipids by the action of phospholipase A(2). Lysophospholipids, the other products of phospholipase A(2) reactions, are either reacylated or metabolized to platelet-activating factor. Under normal conditions, these metabolites play important roles in synaptic function, cerebral blood flow regulation, apoptosis, angiogenesis, and gene expression. Increased activities of cyclooxygenases, lipoxygenases, and epoxygenases under pathological situations such as ischemia, epilepsy, Alzheimer's disease, Parkinson disease, amyotrophic lateral sclerosis, and Creutzfeldt-Jakob disease produce neuroinflammation involving vasodilation and vasoconstriction, platelet aggregation, leukocyte chemotaxis and release of cytokines, and oxidative stress. These are closely associated with the neural cell injury which occurs in these neurological conditions. The metabolic products of docosahexaenoic acid, through these enzymes, generate a new class of lipid mediators, namely docosatrienes and resolvins. These metabolites antagonize the effect of metabolites derived from arachidonic acid. Recent studies provide insight into how these arachidonic acid metabolites interact with each other and other bioactive mediators such as platelet-activating factor, endocannabinoids, and docosatrienes under normal and pathological conditions. Here, we review present knowledge of the functions of cyclooxygenases, lipoxygenases, and epoxygenases in brain and their association with neurodegenerative diseases.

Cannabinoid receptors and endocannabinoids: evidence for new players

It is now well established that the psychoactive effects of Cannabis sativa are primarily mediated through neuronal CB1 receptors, while its therapeutic immune properties are primarily mediated through CB2 receptors. Two endocannabinoids, arachidonoylethanolamide and 2-arachidonoylglycerol, have been identified, their action on CB1 and CB2 thoroughly characterized, and their production and inactivation elucidated. However, many significant exceptions to these rules exist. Here we review the evidence suggesting that cannabinoids can modulate synaptic transmission, the cardiovascular system, and the immune system through receptors distinct from CB1 and CB2, and that an additional "independent" endocannabinoid signaling system that involves palmitoylethanolamide may exist.

Enzymes of porcine brain hydrolyzing 2-arachidonoylglycerol, an endogenous ligand of cannabinoid receptors

Anandamide and 2-arachidonoylglycerol (2-AG) are two endogenous ligands for the cannabinoid receptors, and their cannabimimetic activities are lost when they are hydrolyzed enzymatically. Cytosol and particulate fractions of porcine brain exhibited a high 2-AG hydrolyzing activity of 100 nmol/min/mg protein. Most of the activity could be attributed to a monoacylglycerol lipase-like enzyme that did not hydrolyze anandamide. It was separated by hydroxyapatite chromatography from anandamide amidohydrolase, which is also capable of hydrolyzing 2-AG as well as anandamide. Thus, porcine brain has at least two enzymes capable of hydrolyzing 2-AG. The 2-AG hydrolase activities of both the cytosolic and particulate enzymes were irreversibly and time-dependently inhibited by methyl arachidonyl fluorophosphonate with IC50 values as low as 2-3 nM.

Metabolic fate of exogenous diacylglycerols in A10 smooth muscle cells

The metabolic fate of exogenous diacylglycerols, 1-palmitoyl-2-[1-14C]oleoyl-sn-glycerol (2-[14C]POG) and 1-stearoyl-2-[1-14C]arachidonoyl-sn-glycerol (2-[14C]SAG), was determined after incubation of A10 smooth muscle cells with liposomal suspensions. Hydrolysis through a diacylglycerol (DG) lipase pathway was the predominant metabolic fate; more than 80% of cell-associated radioactivity from 2-[14C]POG and 2-[14C]SAG was recovered in lipolytic products, monoacylglycerol (MG) and fatty acids (FA), which were present in the incubation medium. Hydrolysis of 2-[14C]POG was reduced completely by tetrahydrolipstatin, a lipase inhibitor. Very little radioactivity from either 2-[14C]POG or 2-[14C]SAG was incorporated into triacylglycerol or phospholipids. DG lipase and kinase activities were measured by in vitro enzyme assays. 1-[1-14C]Palmitoyl-2-oleoyl-sn-glycerol (1-[14C]POG) was phosphorylated (kinase activity) to a greater extent than 2-[14C]SAG in assays with both soluble and particulate subcellular fractions from A10 cells. DG lipase activity (hydrolysis of 1-[14C]POG and 2-[14C]SAG) was markedly stimulated by the addition of 20 mM MgCl2 and 20 mM ATP to the assay. Under optimal assay conditions, DG lipase activity exhibited little substrate specificity. Our findings indicate that exogenous DG are mainly hydrolyzed by DG and MG lipases in A10 smooth muscle cells; as a result, signalling mechanisms responding to DG second messengers will be attenuated.

Purification of lipases, phospholipases and kinases by heparin-Sepharose chromatography

Heparin interacts with lipases, phospholipases and kinases. Immobilized heparin can be used for the purification of diacylglycerol and triacylglycerol lipases, phospholipases A2 and C and protein and lipid kinases. The use of heparin-Sepharose is an important development in analytical and preparative techniques for the separation and isolation of lipases, phospholipases and kinases.

Effects of glycosaminoglycans and glycosphingolipids on cytosolic phospholipases A2 from bovine brain

Two forms of Ca(2+)-independent cytosolic phospholipase A2 activity (110 kDa and 39 kDa) were found in bovine brain. They were separated by Sephadex G-75 column chromatography. The 110 kDa phospholipase A2 was much more active with phosphatidylethanolamine and was not affected by glycosaminoglycans, whereas the 39 kDa phospholipase A2 was much more active with ethanolamine plasmalogen and was markedly inhibited by glycosaminoglycans. Heparan sulphate was the most potent inhibitor, followed by chondroitin sulphate, hyaluronic acid and heparin. Gangliosides, especially the GM3 ganglioside, but not other glycosphingolipids, inhibited the activity of the 39 kDa phospholipase A2 in a dose-dependent manner. The heat-inactivation profiles of the 110 kDa and 39 kDa phospholipases A2 provide further evidence for the differences between these cytosolic enzymes. Interactions between glycosaminoglycans, gangliosides and phospholipases A2 may be involved in the maintenance of membrane function.

Partial purification of a diacylglycerol lipase from bovine aorta

A diacylglycerol (DG) lipase has been purified from a soluble subcellular fraction of bovine aorta by (NH4)2SO4 precipitation in the presence of 5.0% (w/v) Triton X-100, followed by chromatography on DEAE-Sephacel, heparin-Sepharose and octyl-Sepharose in the presence of either CHAPS or Triton X-100 detergents. Under basal conditions, the hydrolysis of a short-chain [3H]dioctanoylglycerol ([3H]diC8) substrate was much greater than that of a long-chain 1-[1-14C]palmitoyl-2-oleoyl-sn-glycerol (1-[14C]POG) substrate. Lipase activity measured with 1-[14C]POG was markedly enhanced by Triton X-100. In the presence of 0.1% Triton X-100, specific enzyme activities in the octyl-Sepharose fraction determined with 1-[14C]POG or 1-stearoyl-2-[1-14C]-arachidonoyl-sn-glycerol as substrates were the same as that measured with [3H]diC8. MgCl2 (5mM) or CaCl2 (2 mM) also selectively stimulated lipase activity (up to 10-13-fold) measured with the long-chain (1-[14C]POG) substrate only. The increase in relative specific activity in the octyl-Sepharose fraction was 60-fold and 155-fold, based on hydrolysis of [3H]diC8 and 1-[14C]POG (+ Triton X-100), respectively. Unlabelled diC8 was a competitive inhibitor of 1-[14C]POG hydrolysis, suggesting that a single lipase hydrolyses both the short-chain and long-chain DG substrates; selective stimulatory effects of non-ionic detergents and bivalent cations on the hydrolysis of 1-[14C]POG may be due to effects on the physical properties of the substrate preparation. Monoacylglycerol lipase, DG kinase and cholesterol esterase activities could not be detected in the partially purified lipase preparation.

Mobilization of diacylglycerol in intact HeLa cells by exogenous phospholipase C from Cl. perfringens is accompanied by release of fatty acids including arachidonic acid

The second messenger diacylglycerol (DAG), chiefly derived from phosphatidylcholine (PC) or from phosphatidylinositol (PI), through the activation of specific phospholipases C (PLC), plays a key role in cellular stimulation. The activation of a particular PLC was simulated in intact HeLa cells by treatment with exogenous PC-PLC (Cl. perfringens) or with PI-PLC (B. cereus). Both enzymes rapidly mobilized DAG. However, only PC-PLC led, in Hela cells, to morphological changes (which were reversible on enzyme removal within the time frame of the experiments) and to an increase of intracellular calcium concentration with a lag of > 10 min. In cells prelabeled with [1-14C]arachidonic acid only PC-PLC but not PI-PLC induced the release of labeled fatty acid with a lag of > 10 min. Upon prelabeling of cells with [1-14C]oleic acid, PC-PLC led to a release of radioactive oleic acid. The release of arachidonic acid (AA) required a threshold dose of PC-PLC and a minimum time of treatment beyond which the AA release continued for a certain period, even in the absence of the exogenous enzyme. Under the conditions used, neither PLA2 nor DAG lipase activity were detectable in the PC-PLC preparation. Therefore, AA release was due to activation of a cellular enzyme, probably cellular PLA2 activity. The PC-PLC-induced AA release could be inhibited to a certain extent by EGTA and by quinacrine but not by the glucocorticoid fluocinolone acetonide. Only PC-PLC (but not PI-PLC) caused, in addition, an increase of the level of monoglycerol, which paralleled the appearance of AA. An increase of labeled monoglycerol was detectable in HeLa cells prelabeled with radioactive oleic acid or with 1-[1-14C]palmitoyl-lyso-PC but not in cells prelabeled with radioactive AA, thus indicating that the fatty acid originated from sn-2 position of the glycerol moiety. The 1-monoacylglycerol was probably generated from lysophospholipids by the bacterial PC-PLC. This enzyme preparation has been shown to catalyze such breakdown of lysophosphatidylcholine in vitro. PC-PLC-induced AA release occurred also after down-regulation of protein kinase C by an overnight pretreatment with phorbol ester TPA (TPA-pretreated cells, but not control cells, on treatment with PC-PLC, metabolized AA to prostaglandins).(ABSTRACT TRUNCATED AT 400 WORDS)

Diacylglycerol metabolism in neonatal rat liver: characterization of cytosolic diacylglycerol lipase activity and its activation by monoalkylglycerols

Diacylglycerol lipase (glycerol ester hydrolase, EC 3.1.1.3) activities were investigated in subcellular fractions from neonatal and adult rat liver in order to determine whether one or more different lipases might provide the substrate for the developmentally expressed, activity monoacylglycerol acyltransferase. The assay for diacylglycerol lipase examined the hydrolysis of sn-1-stearoyl,2- [14C]oleoylglycerol to labeled monoacylglycerol and fatty acid. Highest specific activities were found in lysosomes (pH 4.8) and cytosol and microsomes (pH 8). The specific activity from plasma membrane from adult liver was 5.8-fold higher than the corresponding activity in the neonate. In other fractions, however, no developmental differences were observed in activity or distribution. In both lysosomes and cytosol, 75 to 90% of the labeled product was monoacylglycerol, suggesting that these fractions contained relatively little monoacylglycerol lipase activity. In contrast, 80% of the labeled product from microsomes was fatty acid, suggesting the presence of monoacylglycerol lipase in this fraction. Analysis of the reaction products strongly suggested that the lysosomal and cytosolic diacylglycerol lipase activities hydrolyzed the acyl-group at the sn-1 position. The effects of serum and NaCl on diacylglycerol lipase from each of the subcellular fractions differed from those effects routinely observed on lipoprotein lipase and hepatic lipase, suggesting that the hepatic diacylglycerol lipase activities were not second functions of these triacylglycerol lipases. Cytosolic diacylglycerol lipase activity from neonatal liver and adult liver was characterized. The apparent Km for 1-stearoyl,2-oleoylglycerol was 115 microM. There was no preference for a diacylglycerol with arachidonate in the sn-2 position. Bovine serum albumin stimulated the activity, whereas dithiothreitol, N-ethylmaleimide, and ATP inhibited the activity. Both sn-1(3)- and 2-monooleylglycerol ethers stimulated cytosolic diacylglycerol lipase activity 2-3-fold. The corresponding amide analogs stimulated 28 to 85%, monooleoylglycerol itself had little effect, and 1-alkyl- or 1-acyl-lysophosphatidylcholine inhibited the activity. These data provide the first characterization of hepatic subcellular lipase activities from neonatal and adult rat liver and suggest that independent diacylglycerol and monoacylglycerol lipase activities are present in microsomal membranes and that the microsomal and cytosolic diacylglycerol lipase activities may describe an ambipathic enzyme. The data also suggest possible cellular regulation by monoalkylglycerols.

Diacylglycerol generated in the phospholipid vesicles by phospholipase C is effectively utilized by diacylglycerol lipase in rat liver cytosol

Diacylglycerol was generated in phosphatidylcholine vesicles by incubation with Clostridium welchii phospholipase C. Newly formed diacylglycerol was rapidly converted to monoacylglycerol and glycerol when rat liver cytosol fraction was present in the incubation mixture, suggesting the presence of di- and monoacylglycerol lipase activities in this subcellular fraction. On the other hand, 3H-labeled diacylglycerol co-emulsified with non-radioactive phosphatidylcholine was found to be a poor substrate for the diacylglycerol lipase. These results indicate that enzymatic generation of diacylglycerol provide a substrate having a suitable physical state for the expression of diacylglycerol lipase activity. It was also found that the rate of diacylglycerol hydrolysis was dependent upon the rate of diacylglycerol generation, but not upon the absolute concentration in the incubation mixture. When the rate of diacylglycerol hydrolysis was plotted against the rate of diacylglycerol generation, a saturation curve was obtained and the double-reciprocal plot gave a straight line. It is not known why a relationship similar to Michaelis-Menten type kinetics was obtained between the rate of diacylglycerol hydrolysis and diacylglycerol generation instead of diacylglycerol concentration, but it may be best explained by the following assumptions: (1) diacylglycerol molecules are generated at the surface of the lipid vesicles where they are readily accessible to diacylglycerol lipase; (2) soon after the generation, diacylglycerol molecules migrate into inside the vesicles where they are inaccessible to the enzyme; (3) the effective concentration of diacylglycerol, i.e., the concentration of diacylglycerol located in the surface layer of the vesicles is proportional to the rate of diacylglycerol generation.

Rapid hydrolysis of diacylglycerol formed during phosphatidate phosphatase assay by lipase activities in rat liver cytosol and microsomes

Side reactions which may affect the determination of phosphatidate phosphatase activity were investigated in rat liver cytosol and microsomes. Incubation of these subcellular fractions with either 14C-labeled phosphatidate bound to microsomal membranes (PAmb) or that coemulsified with microsomal lipids resulted in rapid formation of water-soluble products, most of which were identified as glycerol, in addition to diacylglycerol. Neither lysophosphatidate nor glycerol 3-phosphate accumulated under any of the conditions used and only a minute amount of activity catalyzing hydrolysis of glycerol 3-phosphate could be detected in cytosol and microsomes, suggesting that glycerol was not formed by the deacylation of phosphatidate to glycerol 3-phosphate and subsequent dephosphorylation. On the other hand, pretreatment of cytosol or microsomes with diisopropylfluorophosphate abolished the formation of water-soluble products, indicating that glycerol was formed from diacylglycerol, the product of the phosphatidate phosphatase reaction, by lipase-type activities. Rapid deacylation of diacylglycerol by these subcellular fractions was also observed with an emulsion of phosphatidate, which has been purified from the total lipid extract of PAmb as substrate. The rate of hydrolysis of diacylglycerol was maximum when the concentration of diacylglycerol was less than 20 microM with either cytosol or microsomes. The present results suggest that it is essential to characterize the reaction products before employing specific assay conditions for phosphatidate phosphatase. At least under the conditions we tested, reliable measurement of the enzyme activity in rat liver cytosol and microsomes can be achieved only by determining the release of Pi or that of water-soluble activity from 32P-labeled phosphatidate.

Mono- and diacylglycerol lipases in spinal cord of lean and obese Zucker rats

1. Genetically obese Zucker rats (fa/fa) contain 2-3 times higher activities mono- and diacylglycerol lipases in their spinal cords than their lean littermates. 2. When rats were exercised (1 hr daily, 5 days/week) on a treadmill for 6 months, there was a decrease of about 30% (P less than 0.05) in the activities of mono- and diacylglycerol lipases in lean rats but not in obese animals. 3. High activities of lipases in Zucker obese rats may be related to the elevated levels of beta-endorphin present in these animals. 4. The activities of arylsulfatase, beta-N-acetylhexosaminidase and alkaline phosphatase, tested to check the stability of spinal cord extracts, were similar in lean and obese rat spinal cords.

Composition and genetic variability of heparin-sepharose CL-6B protein fractions obtained from the solubilized proteins of mouse organs

The solubilized proteins of liver and brain from mice of two inbred strains (C57BL/6J and DBA/2J) and their hybrids were subfractionated by heparin Sepharose (H-S) CL-6B affinity chromatography. The H-S binding and nonbinding proteins were separated by two-dimensional electrophoresis. The protein patterns obtained were analyzed with regard to their protein composition and their genetic variability (qualitative and quantitative variants). Eighty to ninety percent of the H-S binding proteins were unique to this class of proteins. This class was rich in organ-specific proteins. Compared to the nonbinding proteins the portion of basic proteins was only slightly increased, suggesting that most of the H-S binding proteins interact specifically with heparin. The frequency of qualitative protein variants revealed that H-S binding proteins are more conservative than H-S nonbinding proteins. The quantitative genetic variability was higher in liver than in brain. Quantitative protein variants occurred more frequently than qualitative variants.

Characterization and solubilization of membrane bound diacylglycerol lipases from bovine brain

Bovine brain contains two diacylglycerol lipases. One is localized in purified microsomes and the other is found in the plasma membrane fraction. The microsomal enzyme is markedly stimulated by the non-ionic detergent, Triton X-100, and Ca2+, whereas the plasma membrane diacylglycerol lipase is strongly inhibited by Triton X-100 and Ca2+ has no effect on its enzymic activity. Both enzymes were solubilized using 0.25% Triton X-100. The solubilized enzymes followed Michaelis-Menten kinetics. The apparent Km values for microsomal and plasma membrane enzymes are 30.5 and 12.0 microM respectively. Both lipases are strongly inhibited by RHC 80267, with Ki values for microsomal and plasma membrane diacylglycerol lipases of 70 and 43 microM, respectively. The retention of microsomal diacylglycerol lipase on a concanavalin A-Sepharose column and its elution by methyl alpha-D-mannoside indicates the glycoprotein nature of this enzyme.