The Biosynthesis of ß-Hydroxy-ß-methylglutaryl Coenzyme A in Yeast
V. THE ROLE OF ACYL CARRIER PROTEIN
Harry Rudney 1, Peter R. Stewart 1, Philip W. Majerus 1, and P. Roy Vagelos 1
From the
1 From the Department of Biochemistry, Western Reserve University School of Medicine, Cleveland, Ohio, and the Laboratory of Biochemistry, National Heart Institute, Bethesda, Maryland
In the presence of catalytic amounts of the ß-hydroxy-ß-methylglutaric acid coenzyme A-condensing enzyme of yeast, substrate amounts of acetoacetyl acyl carrier protein and acetyl coenzyme A react to form stoichiometric amounts of protein-bound ß-hydroxy-ß-methylglutaric acid, which is apparently ß-hydroxy-ß-methylglutaric acid acyl carrier protein. The condensation reaction with acetoacetyl acyl carrier protein proceeds at about one-sixth the rate observed with acetoacetyl coenzyme A. ß-Hydroxy-ß-methylglutaric acid coenzyme A does not undergo a transacylation reaction with acyl carrier protein, but a nonenzymatic transacylation of ß-hydroxy-ß-methylglutaric acid acyl carrier protein to coenzyme A does occur. These observations agree with previous suggestions that the thioester bond of the acetoacyl moiety remains intact during the condensation reaction with acetyl coenzyme A and provide a basis for unification of the so called malonate and acetate pathways of ß-hydroxy-ß-methylglutaric acid synthesis.
Submitted on August 2, 1965
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