Inhibition of the malic enzyme from Acinetobacter calcoaceticus by NADPH and NADH]

The malic enzyme enriched from Acinetobacter calcoaceticus is inhibited by NADPH and NADH. The inhibition afforded by the reduced coenzymes is not affected by NAD+, AMP and 3'.5'-AMP. Against L-malate, NADPH inhibits the enzyme in a noncompetitive linear fashion (Ki = 1.5 x 10(-4) M), against NADP+, competitively linearly (Ki = 5.0 x 10(-5) M). While NADPH acted as a product inhibitor, NADH seems to be an allosteric effector of the malic enzyme, because with L-malate as the variable substrate in the double reciprocal plot, a nonlinear curve is obtained.     

Inhibition of lysosomal enzyme liberation by indomethacin in vivo

The volume of the peritoneal exudate induced in the rat by iota carrageenan is reduced by subcutaneous administration of indomethacin while the concentrations of three lysosomial enzymes in the exudate are slightly increased or not modified. Thus, the total enzymatic activities of the exudate are reduced by indomethacin. The leucocyte accumulation remains unchanged in the indomethacin treated rats. During the development of the peritoneal exudate, the circulating plasma displays a high degree of lysosomial enzymes activity which is suppressed by indomethacin at the dose of 4 mg/kg.     

Regulation of hepatic malic enzyme by perfluorodecanoic acid

Perfluorodecanoic acid (PFDA) administration to adult male rats increased both the activity of hepatic malic enzyme and liver weight in a dose-dependent manner. Hepatomegaly and augmented activity of malic enzyme in liver were apparent within one day following PFDA administration and reached a plateau by three days posttreatment. Malic enzyme quantity per liver in PFDA-treated rats was elevated within one day following dosing and increased continually throughout five days posttreatment. Administration of PFDA to rats in the fed state also led to an increase in the specific activity of hepatic malic enzyme that peaked at three days following dosing. When compared to the fed condition, rats fasted for 48 hours had a decrease in both relative liver weight and the quantity of supernatant protein per liver. The total activity (U/liver) and specific activity of malic enzyme in the liver were also reduced in the fasted state. During the 24 hours after treatment in rats fasted for 48 hours, the body weight as well as the absolute and relative liver weight of animals receiving vehicle declined continuously in the absence of feed. Following the administration of PFDA to fasted rats, body weight was maintained until eight hours posttreatment but then declined at a rate similar to that found with the vehicle-treated group. Absolute and relative liver weight in PFDA-treated rats were increased significantly at eight hours posttreatment when compared to those receiving vehicle, and this increment was maintained throughout the rest of the 24 hours following dosing. While the activity and enzyme content of hepatic malic enzyme decreased in the vehicle-treated group, administration of PFDA to rats fasted for 48 hours prevented their decline. The specific activity of hepatic malic enzyme in 48 hours fasted rats receiving PFDA was also elevated significantly at 16 hours posttreatment. Thus, the administration of PFDA to the adult male rat in both the fed and fasted nutritional states was found to regulate hepatic malic enzyme by not only increasing enzyme quantity but also by augmenting the specific activity, (ie, catalytic state) of the enzyme.     

Mitochondrial malic enzyme in human leukocytes

Leukocyte samples from 316 unrelated blood donors were screened for malic enzyme (MEM). The frequency of the common allele in this investigation was MEM1 = 0.63. There is evidence for the existence of a rare fourth allele MEM4.     

Purification of pigeon liver malic enzyme by affinity chromatography

A simple and rapid method for the purification of malic enzyme (EC 1.1.1.40) from pigeon liver is described. Malic enzyme in the crude tissue extract was partially purified by heat treatment, ammonium sulfate fractionation, and DEAE-cellulose chromatography. Final purification was achieved by affinity chromatography on immobilized N⁶-(6-aminohexyl)-adenosine 2′,5′-bisphosphate. Apparently homogeneous enzyme was obtained in 2 days with 54% yield.     

High malic enzyme activity in tumor cells and its cross-reaction with antipigeon liver malic enzyme serum

Summary Rabbit antibodies against pigeon liver malic enzyme (EC 1.1.1.40) were prepared. The antiserum gave single precipitation line with crude pigeon liver extract. Cross reaction was observed with partially purified malic enzyme or crude extract from chicken liver. Positive cross reaction was also observed with the concentrated cytosolic fraction of two human carcinoma cell lines which were demonstrated to contain high malic enzyme activity. All other proteins examined did not react with the antibodies. When purified pigeon liver malic enzyme was mixed with the antiserumin vitro, a time-dependent inactivation of the enzyme activity was observed. Protection of the enzyme activity against antiserum inactivation was afforded by NADP⁺ orL-malate. Metal Mn²⁺ gave little protection.     

Inhibition of mitochondrial ATPase by dicarbopolyborate,a new enzyme inhibitor

Polyborate anions were found to inhibit mitochondrial ATPase. Mercapto and chloro derivatives of dicarbononaborates showed full inhibition of the enzyme activity at 0.5–0.8 mM. The inhibitory effect of dodecaborates was lower. The inhibition was of competitive type with respect to ATP. The inhibition of soluble F₁-ATPase indicates a direct interaction of the polyborate anion with the catalytic part of the enzyme molecule.     

Crithidia fasciculata: regulation of aerobic fermentation by malic enzyme

Aerobic fermentation, described in many protozoan organisms, was investigated using the nonpathogenic protozoan Crithidia fasciculata. The major end-products of this process were organic acids, particularly succinic acid. Inhibition of malic enzyme (EC 1.1.1.40) (l-malate: NADP oxidoreductase (decarboxylating) appeared to be integral to the aerobic fermentative process; the enzyme was inhibited in a cumulative manner by oxalacetate, acetyl-coenzyme A and oxalate. Inhibition by oxalate was noncompetitive with respect to both substrate and coenzyme. The inhibition of malic enzyme by oxalacetate and acetyl-coenzyme A appeared to provide a mechanism for the diversion of carbon from oxalacetate to succinate via the fumarase, thereby avoiding recycling to pyruvate. This was corroborated by the demonstration of an inverse relationship between the concentrations of pyruvate and succinate elaborated by this organism.     

Tissue-specific regulation of two functional malic enzyme mRNAs by triiodothyronine

Rat liver malic enzyme (ME) synthesis is known to be regulated by 3,5,3'-triiodo-L-thyronine (T3). Hybridization of 32P-labeled ME cDNA with RNA extracted from normal and T3-induced livers (15 or 50 micrograms/100 g body weight for 10 days) showed an increase in the ME mRNA concentration by approximately 11-fold in T3-treated rats. ME activity and ME mass were stimulated to the same degree as ME mRNA. Northern blot analysis of either total or poly(A+) RNA revealed two distinct ME mRNAs (21 and 27 S) which were equally induced by T3 treatment. Both mRNAs were shown by in vitro translation assay to program the synthesis of the same immunoprecipitable protein corresponding to full-sized ME. From all the above, we concluded that both messages code for active enzyme. ME activity and ME mRNA were also detected in nonhepatic tissues for which different responses to T3 induction were observed without direct correlation with their respective content of T3 nuclear receptor. Increases in ME activity and level of hybridizable ME mRNA were seen 48 h after a single administration of T3 (200 micrograms/100 g body weight) in liver, kidney, and heart (10.3- and 15.5-, 1.7- and 2.6-, and 1.72- and 3.4-fold above basal values, respectively). Lower levels of induction could already be detected after 24 h, liver being the most stimulated tissue. ME was not affected in brain, lung, testis, and spleen. Northern blot analysis showed that both ME mRNAs are present in all tissues tested, although in different relative proportions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Polymorphism of erythrocyte malic enzyme in the goat

Three electrophoretic variants of erythrocyte malic enzyme (ME) in goats were reported. Inheritance data indicate that they are controlled by codominant alleles. The allele frequencies in four Mediterranean populations are given.