Reaction of chloroacetyl-CoA with rabbit fatty acid synthase. A new method to label specifically and quantify pantetheine prosthetic groups.

The substrate analogue chloroacetyl-CoA inhibits fatty acid synthase by reacting with the 'central' or pantetheine thiol and not the 'peripheral' or beta-ketoacylsynthase thiol as previously reported. This was demonstrated by the isolation of [14C]carboxymethylcysteamine after acid hydrolysis of enzyme labelled with chloro[14C]acetyl-CoA, and by the demonstration that more than one of the partial reactions is inhibited. This reagent now represents a simple and convenient tool both for quantification of the pantetheine thiol and for labelling this site for peptide mapping and isolation.