Two functional domains of coenzyme A activate catalysis by coenzyme A transferase. Pantetheine and adenosine 3‘-phosphate 5‘-diphosphate.

Abstract

Studies of the reactivity of succinyl-CoA:3-keto acid CoA transferase with a small coenzyme A analog, methylmercaptopropionate, have shown that noncovalent interactions between the enzyme and the side chain of CoA are responsible for a rate acceleration of approximately 10(12), which is close to the total rate acceleration brought about by the enzyme (Moore, S. A., and Jencks, W. P. (1982) J. Biol. Chem. 257, 10893-10907). We report here that interaction between the enzyme and the pantetheine moiety of CoA provides the majority of the rate acceleration and destabilization of the enzyme-thiol ester intermediate that is observed with CoA substrates. The role of the adenosine 3'-phosphate 5'-diphosphate moiety of CoA is to provide 6.9 kcal/mol of binding energy in order to pull the pantetheine moiety into the active site. The enzyme-thiol ester intermediate, E-pantetheine, was generated by reaction of pantetheine with the thiol ester of enzyme and methylmercaptopropionate. E-Pantetheine undergoes hydrolysis with khyd = 2 min-1, 140-fold faster than E-CoA, and reacts with acetoacetate with kAcAc = 3 X 10(6) M-1 min-1, only 10-fold slower than E-CoA. However, in the reverse direction acetoacetylpantetheine reacts with CoA transferase (kAcAc-SP = 220 M-1 min-1) 1.6 X 10(6) times slower than acetoacetyl-CoA. The equilibrium constant for the reaction of pantetheine with E-CoA is approximately 8 X 10(-6).