Acetoacetyl-coenzyme A

The introduction to Section 26 8 pointed out that mevalonic acid is the biosynthetic pre cursor of isopentenyl pyrophosphate The early steps m the biosynthesis of mevalonate from three molecules of acetic acid are analogous to those m fatty acid biosynthesis (Sec tion 26 3) except that they do not involve acyl earner protein Thus the reaction of acetyl coenzyme A with malonyl coenzyme A yields a molecule of acetoacetyl coenzyme A... 

Carbon-carbon bond formation then occurs between the ketone carbonyl of acetoacetyl coenzyme A and the a carbon of a molecule of acetyl coenzyme A... 

Succinyl coenzyme A 3-oxo acid transferase catalyses the transformation of ACAC into acetoacetyl coenzyme A in the mitochondria of extra-hepatic tissues. This enzyme defect may be suggested in cases of severe ketoacidosis often associated with neurologic dysfunction [16]. 

Acetyl coenzyme A Acetoacetyl coenzyme A Palmitoyl coenzyme A... 

Vollack, K.U. and Bach, T.J. (1996) Cloning of a cDNA encoding cytosolic acetoacetyl-coenzyme A thiolase from radish by functional expression in Saccharomyces cere-visiae. Plant Physiol., Ill, 1097-107. 

Concomitant to the enhancement of the signal for C-3 in the C NMR spectrum, the signals for H2 and H4 decreased in the H-NMR spectrum of all the tropine moieties compared with those in authentic samples. This indicates the incorporation of deuterium at C2 and C4 derived from C Hj CXX)". As the diminution of the signals for H2 and H4 was not identical at both positions, we suppose a sequential incorporation of labeled acetate (example given in Fig. 15b). From these data we assume that the biosynthesis from N-methyl-pyrrolidinium ion to tropine is a two-step process which does not involve a four carbon unit (acetoacetyl coenzyme A) but two units of acetyl coenzyme A, which were added sequentially as has been suggested for the biosynthesis of cocaine [28, 37]. On the other hand it has been reported that l,2- C2-acetate was incorporated with an equal efficiency at C2 and C4 by non-transformed root cultures of H. albus [36]. Further investigations are required to clarify this matter. 

The origin of C-2 and C-4 has also been proved by the tracer technique as coming from acetate methyl, while for C-3 the carboxyl of acetic acid is the precursor (83), probably via acetoacetyl coenzyme A. The question still open is how ornithine reacts with that compoimd to account for the... 

The study of the reactions of amino sugars with /3-keto thiolesters was undertaken in order to obtain data on the way in which simple models of (S-acetoacetyl-Coenzyme A may react. There is no difference between the modes of reaction of ethyl thiolacetoacetate and ethyl acetoacetate with 2-amino-2-deoxy-D-glucose. In the reaction with l-amino-l-deoxy-o-fructose, the product (18) of the thiolester liberates ethanethiol very readily and forms the lactone (27). amino sugar interact, giving lactone (27). No compound similar to the pyrrole thiolester (18) was found. In this context, the investigation of similar reactions with acetamido sugars will be of interest. 

Acetoacetic ester synthesis, 839—841, 850. See also Ethyl acetoacetate Acetoacetyl acyl carrier protein, 1021 Acetoacetyl coenzyme A, 1021, 1032 Acetone... 

The incorporation of malonate into mevalonic acid and steroids has been investigated further. Experiments with normal and tumorous rats have demonstrated the previously unsuspected fact that the S-methyl group of methionine is incorporated into cholesterol and cholest-7-en-3jS-ol. Some of the enzymes involved in mevalonate synthesis have been isolated. Yeast acetoacetyl coenzyme A thiolase (EC 2.3.1.9) has a molecular weight of about 190 000 and 3-hydroxy-3-methyl glutaryl coenzyme A synthetase (EC 4.1.3.5) a molecular weight of 130 000. Rat liver 3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.34) used only [4/ - H]NADPH in the formation of mevalonic acid with incorporation of two tritium atoms (at Hp and Hp) (see Scheme 1). 

Cai G., Driscoll B.T. and Charles T.C., 2000, Requirement for the enzymes acetoacetyl Coenzyme A synthase and Poly-3-hydroxybutyrate (PHB) synthase for growth of Sinorhizobium meliloti and PHB cycle interm iates. J. Bacteriol. 182 2113-2118. 

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