Malic enzyme and

Both dehydrogenases of the pentose phosphate pathway can be classified as adaptive enzymes, since they increase in activity in the well-fed animal and when insulin is given to a diabetic animal. Activity is low in diabetes or starvation. Malic enzyme and ATP-citrate lyase behave similarly, indicating that these two enzymes are involved in lipogenesis rather than gluconeogenesis (Chapter 21). 

Mitochondria from body wall muscle and probably the pharynx lack a functional TCA cycle and their novel anaerobic pathways rely on reduced organic acids as terminal electron acceptors, instead of oxygen (Saz, 1971 Ma et al, 1993 Duran et al, 1998). Malate and pyruvate are oxidized intramitochondrially by malic enzyme and the pyruvate dehydrogenase complex, respectively, and excess reducing power in the form of NADH drives Complex II and [3-oxidation in the direction opposite to that observed in aerobic organelles (Kita, 1992 Duran et al, 1993 Ma et al,... 

FIGURE 21-9 Production of NADPH. Two routes to NADPH, catalyzed by (a) malic enzyme and (b) the pentose phosphate pathway. 

Nathan, H. A., Induction of Malic Enzyme and Oxaloacetate Decarbox-... 

The activities of cytoplasmic enzymes, such as aspartase, glutamate, oxaloacetate, malic enzyme, and alcohol dehydrogenase (ADH) decrease at the onset of anaerobiosis, with occasional transient increases on the... 

In recent studies(23,26) attempts were made to normalize the tumor-induced abnormalities in the levels of hepatic enzymes. It is known that catalysts of the urea cycle are induced by high protein diet, while high carbohydrate intake, decreasing the levels of alanine aminotransferase, increases those of malic enzyme and pyruvate kinase. In each case, the same percent change was seen in tumor-bearing and normal adult animals (Table V), so that the tumor-induced defiency of such enzymes seen in rats on a normal diet was also apparent on these altered diets. Hormone treatments,... 

The a-chloroacetamide group has features that are beneficial for undirected ABPP. Its small size does not bias binding elements towards a specific class of enzyme, and it possesses reactivity towards a broad variety of nucleophilic amino acid residues. A library of a-chloroacetamide-based probes were synthesized by Cravatt s group. The binding element in these probes was a dipeptide that was varied with small, large, hydrophobic, and charged side chains, and a biotin or rhodamine tag was appended as a reporter tag. Upon screening of eukaryotic proteomes with this library, many enzymes previously unaddressed by directed ABPP probes were uncovered. These included fatty acid synthase, hydro-xypyruvate reductase, malic enzyme, and the nitrilase superfamily [163, 164]. In contrast to the sulfonate esters, a-chloroacetamides react preferentially with cysteine residues in the proteome. 

Fumarate acts as substrate for an important enzyme complex, fumarate reductase, which occurs in a number of cestodes (698). Fumarate reductase accepts reducing equivalents (NADH or NADPH), generated by malic enzyme, and transfers the electrons to fumarate, which is thus reduced to succinate. The reduction of fumarate to succinate is accompanied by the phosphorylation of ADP, one ATP being produced for each fumarate reduced. This phosphorylation involves the cytochrome chain. Succinate may be excreted or is converted by another enzyme complex, succinate decarboxylase, to propionate and excreted. 

Mitochondrial malate dehydrogenase, decarboxylating (malic enzyme) and transhydrogenase activities of adult Hymenolepis microstoma (Cestoda). Journal of Parasitology, 68 213-20. 

McKelvey, J. R. Fioravanti, C. F. (1984). Coupling of malic enzyme and NADPH NAD transhydrogenase in the energetics of Hymenolepis diminuta (Cestoda). Comparative Biochemistry and Physiology, 77B 737-42. 

All. — (1985). Intramitochondrial localization of fumarate reductase, NADPH->NAD transhydrogenase, malic enzyme and fumarase in adult Hymenolepis diminuta. Molecular and Biochemical Parasitology, 17 253-63. 

A second type of mechanism is illustrated by the malic enzyme and fatty synthetase systems. In such systems the effect of T3 on the accumulation of the specific mRNAs does not seem to depend only on direct gene activation by the T3-nuclear receptor. An amplification post-transcriptional mechanism seems to contribute to the accumulation of the specific mRNAs. Stabilization of the mRNA level is also differently modulated by other hormones and by the diet. 

Hermes JD, Roeske CA, O Leary MH, Cleland WW. Use of multiple isotope effects to determine enzyme mechanisms and intrinsic isotope effects. Malic enzyme and glucose-6-phosphate dehydrogenase. Biochemistry 1982 21 5106-5114. 

NADPH is produced by the malic enzyme and by the pentose phosphate pathway. 

NADPH, which provides the reducing equivalents for fatty acid synthesis, is produced by the inducible malic enzyme and by the inducible enzymes of the pentose phosphate pathway, glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase. 

Gonzalez-Garza, M. T., Matlin, S. A., Mata-Cardenas, B. D., and Said-Femandez, S. (1993b). Entamoeba histolytica Inhibition of malic enzyme and alcohol dehydrogenase by (+/-)-, (+)-, and (—)-gossypol. Arch. Med. Res. 24,183-187. 

The drug has high tendency to bind with various proteins and, therefore, may interfere with the energy metabolism, calcium transport and phosphorylation-dephosphorylation reactions [110]. Walter and co-workers [111-113] have found that suramin inhibits lactate dehydrogenase, malate dehydrogenase, malic enzyme and protein-kinase. Jaffe [114], showed that it also interferes with the folate metabolism of the helminths. 

Carboxylation is, in the first place, a thermodynamic problem. Nature solves this problem by associating the carboxylation with some exergonic process. This may be reduction of a product (as in the case of malic enzyme and isocitrate dehydrogenase), hydrolysis of ATP (as in the case of pyruvate carboxylase), hydrolysis of phosphoenolpyruvate (as in the case of phosphoenolpyruvate carboxylase), or cleavage of a carbon-carbon bond (as in the case of ribulose-bisphosphate carboxylase). 

Calculated from equilibrium constants for malic enzyme and malate dehydrogenase Ref. (12). 

CITRATE LYASE, MALIC ENZYME, AND GLUCOSE 6-PHOSPHATE DEHYDROGENASE... 

Glucagon Liver Increased cAMP, decreased fiructose 2,6-bisphosphate, increased phosphorylase activity, glycogen mobilisation Inhibited accumulation of mRNA for malic enzyme and other lipogenic enzymes... 

Goodtidge, A.G. (1968a). Qtrate-clea vage enzyme, malic enzyme and certain dehydrogenases in embryonic and growing chicks. Biochem. ]., 108, 663-6. 

Morris, S.M., Winberry, L.K., Fisch, J.E., Back, D.W. Goodridge, A.G. (1984). Developmental and nutritional regulation of the messenger RNAs for fatty acid synthase, malic enzyme and albumin in the livers of embryonic and newly-hatched chicks. Mol. Cell Biochem., 64, 63-8. 

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