Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
 5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The phenylpropanoid pathway intermediate p-coumaric acid (4-CA) stimulates expression of the bean (Phaseolus vulgaris L.) chalcone synthase (malonyl-CoA:4-coumaroyl-CoA, EC 2.3.1.74) chs15 gene promoter in electroporated protoplasts of alfalfa (Medicago sativa L.). We have analyzed the effects of 5' deletions, mutations, and competition with promoter sequences in trans on the expression of a chs15 promoter-chloramphenicol acetyltransferase gene fusion in elicited alfalfa protoplasts. Two distinct sequence elements, the H-box (consensus CCTACC(N)7CT) and the G-box (CACGTG), are required for stimulation of the chs15 promoter by 4-CA. Furthermore, a 38-base-pair chs15 promoter sequence containing both cis elements conferred responsiveness to 4-CA on the cauliflower mosaic virus 35S minimal promoter. The H-box and G-box in combination establish the complex developmental pattern of chs15 expression and are also involved in stress induction. Hence, potential internal pathway regulation through feed-forward stimulation by 4-CA operates by modulation of the signal pathways for developmental and environmental regulation.
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PMID:Combination of H-box [CCTACC(N)7CT] and G-box (CACGTG) cis elements is necessary for feed-forward stimulation of a chalcone synthase promoter by the phenylpropanoid-pathway intermediate p-coumaric acid. 140 28

Mitochondria isolated from the livers of sheep and rats were shown to oxidize palmitate, oleate and linoleate in a tightly coupled manner, by monitoring the oxygen consumption associated with the degradation of these acids in the presence of 2mM-L-malate. Rat liver mitochondria oxidized linoleate and oleate at a rate 1.2-1.8 times that of palmitate. Sheep liver mitochondria had a specific activity for the oxidation of palmitate that was 50-80% of that of rats and a specific activity for the oxidation of oleate and linoleate that was 30-40% that of rats. This would indicate that sheep conserved linoleate by limiting its oxidation. Carnitine acyltransferase I (CAT I) actively esterified palmitoyl-CoA and linoleate to carnitine in both rat and sheep liver mitochondria, and in both cases the rate for linoleate was faster than for palmitate. The CAT I reaction in both rat and sheep liver was inhibited by micromolar amounts of malonyl-CoA. With 90 microM-palmitoyl-CoA as substrate, CAT I was inhibited by 50% with 2.5 microM-malonyl-CoA in rats, and in sheep, 50% inhibition was found with all malonyl-CoA concentrations tested (1-5 microM). With 90 microM-linoleate as substrate for CAT I, a much larger difference in response to malonyl-CoA was seen, the rat enzyme being 50% inhibited at 22 microM-malonyl-CoA, whereas sheep liver CAT I was 91% and 98% inhibited at 1 microM- and 5 microM-malonyl-CoA respectively. We propose that malonyl-CoA may act as an important regulator of beta-oxidation in sheep, discriminating against the use of linoleate as an energy-yielding substrate.
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PMID:Oxidative metabolism of long-chain fatty acids in mitochondria from sheep and rat liver. Evidence that sheep conserve linoleate by limiting its oxidation. 397 25

The versatile plant acyltransferase (VPAT) family is a recently identified protein family consisting of acyltransferases involved in secondary metabolism in plants along with numerous homologues with as yet unidentified biochemical functions. Malonyl-CoA:anthocyanin 5-O-glucoside-6' "-O-malonyltransferase of Salvia splendens flowers (Ss5MaT1) is a member of this family that catalyzes the regiospecific transfer of the malonyl group from malonyl-CoA to the 6' "-hydroxyl group of the 5-glycosyl moiety of anthocyanins. To elucidate the mechanism and functional amino acid residues of VPAT family enzymes, steady-state kinetic analyses and site-directed mutagenesis of Ss5MaT1 guided by sequence comparison studies were carried out. On the basis of the results of product and dead-end inhibition studies as well as sequence comparison studies, the kinetic mechanism of Ss5MaT1 could be most consistently described in terms of a ternary complex mechanism in which both substrates and the enzyme form a complex before catalysis can occur, as in the case of chloramphenicol O-acetyltransferase (CAT) and histone acetyltransferase (HAT). Eight polar or ionizable amino acid residues that are invariant among 12 VPAT family enzymes were replaced by alanine, and the mutant enzymes were kinetically characterized. A significant diminution of the k(cat) value was observed with the substitution of His167 (relative k(cat), 0.02%) and Asp390 (<0.01%), strongly suggesting that His167 and Asp390 are very important for catalytic activity. The log k(cat) versus pH plots of the Ss5MaT1-catalyzed malonyl transfer suggested that a deprotonated active site group of pK(a) = 7.0 +/- 0.1 may be involved in the catalytic steps of the "substrate to product" conversion in the ternary enzyme-substrate complex. Taking these lines of evidence together with the suggested similarity of the kinetic and catalytic mechanisms of Ss5MaT1 to those of CAT and HAT, the following Ss5MaT1 mechanism based on general acid/base catalysis was proposed: in the ternary complex, a general base deprotonates the 6' "-hydroxyl group of the anthocyanin substrate, thereby promoting a nucleophilic attack on the carbonyl of the thioester of malonyl-CoA; His167 and Asp390 appear to be involved in the general acid/base mechanism of Ss5MaT1.
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PMID:Proposed mechanism and functional amino acid residues of malonyl-CoA:anthocyanin 5-O-glucoside-6'''-O-malonyltransferase from flowers of Salvia splendens, a member of the versatile plant acyltransferase family. 1257 91

Carnitine acyltransferases catalyze the exchange of acyl groups between carnitine and coenzyme A (CoA). These enzymes include carnitine acetyltransferase (CrAT), carnitine octanoyltransferase (CrOT), and carnitine palmitoyltransferases (CPTs). CPT-I and CPT-II are crucial for the beta-oxidation of long-chain fatty acids in the mitochondria by enabling their transport across the mitochondrial membrane. The activity of CPT-I is inhibited by malonyl-CoA, a crucial regulatory mechanism for fatty acid oxidation. Mutation or dysregulation of the CPT enzymes has been linked to many serious, even fatal human diseases, and these enzymes are promising targets for the development of therapeutic agents against type 2 diabetes and obesity. We have determined the crystal structures of murine CrAT, alone and in complex with its substrate carnitine or CoA. The structure contains two domains. Surprisingly, these two domains share the same backbone fold, which is also similar to that of chloramphenicol acetyltransferase and dihydrolipoyl transacetylase. The active site is located at the interface between the two domains, in a tunnel that extends through the center of the enzyme. Carnitine and CoA are bound in this tunnel, on opposite sides of the catalytic His343 residue. The structural information provides a molecular basis for understanding the catalysis by carnitine acyltransferases and for designing their inhibitors. In addition, our structural information suggests that the substrate carnitine may assist the catalysis by stabilizing the oxyanion in the reaction intermediate.
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PMID:Structure and function of carnitine acyltransferases. 1559 Oct