Malonyl CoA decarboxylase

Also, decarboxylations of malonate-type compounds have been confirmed to proceed with retention of configuration. Indeed, malonyl-CoA decarboxylase from uropygial gland is enantioselective to the substrate as well as the product. Only... 

To clarify the characteristics of AMDase, the effects of some additives were examined using phenylmalonic acid as the representative substrate. The addihon of ATP and coenzyme A did not enhance the rate of the reaction, different from the case of malonyl-CoA decarboxylase and others in those, ATP and substrate acid form a mixed anhydride, which in turn reacts with coenzyme A to form a thiol ester of the substrate. In the present case, as both ATP and CoA-SH had no effect, the mechanism of the reaction will be totally different from the ordinary one described above. It is well estabhshed that avidin is a potent inhibitor of the formation of the biotin-enzyme complex. In the case of AMDase, addition of avidin has no influence on the enzyme activity, indicating that AMDase is not a biotin enzyme. 

The enzymatic reaction was performed at 30 °C for 2 hours in a volume of 1 ml of 250 mM phosphate buffer (pH 6.5) containing 50 mM of KOH, 32 U/ml of the enzyme, and [1- C]-substrate. The product was isolated as the methyl ester. When the (S)-enantiomer was employed as the substrate, C remained completely in the product, as confirmed by C NMR and HRMS. In addition, spin-spin coupling between and was observed in the product, and the frequency of the C-O bond-stretching vibration was down-shifted to 1690 cm" (cf. 1740 cm for C-O). On the contrary, reaction of the (R)-enantiomer resulted in the formation of (R)-monoacid containing C only within natural abundance. These results clearly indicate that the pro-R carboxyl group of malonic acid is ehminated to form (R)-phenylpropionate with inversion of configuration [28]. This is in sharp contrast to the known decarboxylation reaction by malonyl CoA decarboxylase [1] and serine hydroxymethyl transferase [2], which proceeds with retention of configuration. 

As an example, bis(trifluoromethyl) carbinols have been described as strong inhibitors of malonyl-CoA decarboxylase, an enzyme involved in the metabolism of fatty acids, a possible target for the treatment of ischemic heart disease and diabetes (Figure 7.24)." Although few enzymological data are available, it is reasonable to... 

Carnitine acyltransferase 1 is strongly inhibited by malonyl CoA, andmuscle has both acetyl CoA carboxylase, which forms malonyl CoA, and malonyl CoA decarboxylase, which acts to remove malonyl CoA and relieve the inhibition of carnitine acyl transferase. The two enzymes are regulated in opposite directions in response to insulin, which stimulates fatty acid synthesis and reduces /S-oxidation, and glucagon that reduces fatty acid synthesis and increases p-oxidation (Kerner and Hoppel, 2000 Louet et al., 2001 Eaton, 2002). 

MSAS from P. patulum was separated from the FAS via sucrose gradient centrifugation [121,122] and thus shown to constitute a distinct multifunctional enzymatic system. It was purified to homogeneity and found to be a 190 kDa multifunctional enzyme [22,120]. The enzyme was more stable in the presence of its substrates and at mildly basic pH values. The pH optimum of the enzyme was 7.6 and apparent K values for its substrates were 10 pM (acetyl-CoA), 7 pM (malonyl CoA), and 12 pM (NADPH) [115,120,123]. The rate for triacetate lactone formation in the absence of NADPH was determined to be ten-fold lower than for 6-MSA formation (Fig. 5) [120]. Analogous to FASs and peptide synthetases, 4 -phosphopantetheine is a covalently bound cofactor of 6-MSAS [124]. Likewise, iodoacetamide and N-ethylmaleimide were found to inactivate the enzyme, suggesting the presence of catalytic sulfhydryl residues in 6-MSAS [124]. Furthermore, in the presence of malonyl CoA and NADPH, low concentrations of iodoacetamide convert 6-MSAS into a malonyl CoA decarboxylase. Without external addition of acetyl-CoA, 6-MSAS decarboxylates the malonyl group and the derived acetyl moiety is used as a starter unit for the formation of 6-MSA [125]. 

Cheng JF, Huang Y, Penuliar R, Nishimoto M, Lin L, Arrhe- 22. nius T, Yang G, O Leary E, Barbosa M, Barr R, Dyck JRB, Lopaschuk GD, Nadzan AM. Discovery of potent and orally available malonyl-CoA decarboxylase inhibitors as cardioprotective 23. agents. J. Med. Ghent. 2006 49 4055-4058. 

FIG. 4.2 Malate metabolism in mitochondria from body wall muscle of adult Ascaris smm. (1) Fumarase (2) malic enzyme (3) pyruvate dehydrogenase complex (4) complex I (5) succinate-coenzyme Q reductase (complex II, fumarate reductase) (6) acyl CoA transferase (7) methylmalonyl CoA mutase (8) methyl-malonyl CoA decarboxylase (9) propionyl CoA condensing enzyme (10) 2-methyl acetoacetyl CoA reductase (11) 2-methyl-3-oxo-acyl CoA hydratase (12) electron-transfer flavoprotein (13) 2-methyl branched-chain enoyl CoA reductase (14) acyl CoA transferase. 

ACC-2 produces malonyl CoA, which inhibits carnitine palmitoyl transferase I, thereby blocking fatty acid entry into the mitochondria. Muscle also contains malonyl CoA decarboxylase, which catalyzes the conversion of malonyl CoA to acetyl CoA and carbon dioxide. Thus, both the synthesis and degradation of malonyl CoA is carefully regulated in muscle cells to balance glucose and fatty acid oxidation. Both allosteric and covalent means of regulation are employed. Citrate activates ACC-2, and phosphorylation of ACC-2 by the adenosine monophosphate (AMP)-activated protein kinase inhibits ACC-2 activity. Phosphorylation of malonyl CoA decarboxylase by the AMP-activated protein kinase activates the enzyme, further enhancing fatty acid oxidation when energy levels are low. 

Fatty acid uptake by muscle requires the participation of fatty acid-binding proteins and the usual enzymes of fatty acid oxidation. Fatty acyl-CoA uptake into the mitochondria is controlled by malonyl-CoA, which is produced by an isozyme of acetyl-coA carboxylase (ACC-2 the ACC-1 isozyme is found in liver and adipose tissue and is used for fatty acid biosynthesis). ACC-2 is inhibited by phosphorylation by the AMP-activated protein kinase (AMP-PK) such that when energy levels are low the levels of malonyl CoA will drop, allowing fatty acid oxidation by the mitochondria. In addition, muscle cells also contain the enzyme malonyl CoA decarboxylase, which is activated by phosphorylation by the AMP-PK. Malonyl CoA decarboxylase converts malonyl CoA to acetyl CoA, thereby relieving the inhibition of carnitine palmitoyl transferase I (CPT-I) and stimulating fatty acid oxidation (Fig. 47.5). Muscle cells do not synthesize fatty acids the presence of acetyl CoA carboxylase in muscle is exclusively for regulatory purposes. 

Fig. 47.5. Regulation of fatly acyl CoA entry into muscle mitochondria. 1. Acetyl CoA carboxylase-2 (ACC-2) converts acetyl CoA to malonyl CoA, which inhibits carnitine pahnitoyl transferase I (CPT-I), thereby blocking fatty acyl CoA entry into the mitochondria. 2. However, as energy levels drop, AMP levels rise because of the activity of the adenylate kinase reaction. 3. The increase in AMP levels activates the AMP-activated protein kinase (AMP-PK), which phosphorylates and inactivates ACC-2, and also phosphorylates and activates malonyl CoA decarboxylase (MCoADC). The decarboxylase converts malonyl CoA to acetyl CoA, thereby relieving the inhibition of CPT-1, and allowing fatty acyl CoA entry into the mitochondria. This allows the muscle to generate ATP via the oxidation of fatty acids.

Fatty acid uptake into cardiac muscle is similar to that for other muscle cell types and requires fatty acid-binding proteins and carnitine palmitoyl transferase I for transfer into the mitochondria. Fatty acid oxidation in cardiac muscle cells is regulated by altering the activities of ACC-2 and malonyl CoA decarboxylase. 

Fatty acids become the muscle s preferred fuel under starvation conditions. The AMP-PK is active because of lower than normal ATP levels, ACC-2 is inhibited, and malonyl CoA decarboxylase is activated, thereby retaining full activity of CPT-1. 

Park, H. Kaushik, V.K. Constant, S. Prentki, M. Przybytkowski, E. Ruder-man, N.B. Saha, A.K. Coordinate regulation of malonyl-CoA decarboxylase, sn-glycerol-3-phosphate acyltransferase, and acetyl-CoA carboxylase by AMP-activated protein kinase in rat tissues in response to exercise. J. Biol. Chem., 277, 32571-32577 (2002)... 

Creatine biosynthesis defects Lysosomal cystine transport def., infantile Lysosomal cystine transport def, adolescent Hyperoxaluria type 1 Malonyl-CoA decarboxylase def Lysosomal cystine transport def, infantile Lysosomal cystine transport def, adolescent... 

Malonyl-CoA decarboxylase def Ornithine transcarbamylase def Argininosuccinic aciduria Arginase def,... 

Biochemically, malonyl-CoA decarboxylase deficiency is characterised by the excretion of excess malonic and methylmalonic acids in urine, mostly... 

Fig. 8.1. Pathways of 2-ketoglutarate, fumarate, malonate and N-acetylaspartate metabolism and proposed pathways of D- and L-2-hydroxyglutarate metabolism. 8.1, 2-Ketoglutarate dehydrogenase complex (El or E2) 8.2, fumarase 8.3, malonyl-CoA decarboxylase 8.6, aspartoacylase...

FitzPatrick DR, Hill A, Tolmie JL, Thorburn DR, Christodolou J. The molecular basis of malonyl-CoA decarboxylase deficiency. Am J Hum Genet 1999 65 318-326... 

Muscle also has malonyl CoA decarboxylase, which acts to decarboxylate malonyl CoA back to acetyl CoA. Acetyl CoA carboxylase and malonyl CoA decarboxylase are regulated in opposite directions by phosphorylation catalysed by a 5 -AMP-dependent protein kinase (which thus reflects the state of ATP reserves in the cell section 10.2.2.1). Phosphorylation in response to an increase in intracellular 5 -AMP results in ... 

P. E. Kolattukudy, A. 3. Poulose and Y. S. Kim, Malonyl-CoA decarboxylase from avian, mammalian and microbial sources. Methods Enzymol. 71 150 (1981). 

Decarboxylation of malonic acid derivatives is a well studied process in the biosynthesis of biomolecules such as long-chain fatty acids and polyketides. A decarboxylase that exhibits enantioselectivity for substituted malonates would be useful for producing ophcally active carboxylic acids, hi fact, malonyl-CoA decarboxylase does catalyze an enantioselective decarboxylation (Figure 3.2) [5], but malonyl-CoA is an unsuitable precursor for optically active substances. Instead, we focused on the prochiral-activated compoimd arylmalonate, an intermediate of malonic ester synthesis, to develop a method for enantioselective decarboxylation. Malonates are stable at room temperature but readily decompose to arylacetate and CO2 at high temperatures. This suggests that the decarboxylation of arylmalonate may occur naturally if arylmalonate acts as a substrate for a decarboxylase. 

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