title: The importance of the amide bond nearest the thiol group in enzymatic reactions of coenzyme A.
abstract: Analogues of coenzyme A (CoA) and of CoA thioesters have been prepared in which the amide bond nearest the thiol group has been modified. An analogue of acetyl-CoA in which this amide bond is replaced with an ester linkage was a good substrate for the enzymes carnitine acetyltransferase, chloramphenicol acetyltransferase, and citrate synthase, with K(m) values 2- to 8-fold higher than those of acetyl-CoA and V(max) values from 14 to >80% those of the natural substrate. An analogue in which an extra methylene group was inserted between the amide bond and the thiol group showed less than 4-fold diminished binding to the three enzymes but exhibited less than 1% activity relative to acetyl-CoA with carnitine acetyltransferase and no measurable activity with the other two enzymes. Analogues of several CoA thioesters in which the amide bond was replaced with a hemithioacetal linkage exhibited no measurable activity with the appropriate enzymes. The results indicate that some aspects of the amide bond and proper distance between this amide and the thiol/thioester moiety are critical for activity of CoA ester-utilizing enzymes.
authors.affiliation: Department of Chemistry, Stony Brook University, NY 11794-3400, USA.
authors.forename: Jin
authors.initials: J
authors.lastname: Xun
authors.forename: Haidong
authors.initials: H
authors.lastname: Huang
authors.forename: Kurt W
authors.initials: KW
authors.lastname: Vogel
authors.forename: Dale G
authors.initials: DG
authors.lastname: Drueckhammer
mesh_terms: D000105:Acetyl Coenzyme A / Q000031:analogs & derivatives* / Q000138:chemical synthesis; D000577:Amides / Q000737:chemistry*; D003065:Coenzyme A / Q000737:chemistry* / Q000378:metabolism; D004952:Esters / Q000138:chemical synthesis; D015394:Molecular Structure; D013438:Sulfhydryl Compounds / Q000737:chemistry
chemical_list: D000577:Amides; D004952:Esters; D013438:Sulfhydryl Compounds; D000105:Acetyl Coenzyme A; D003065:Coenzyme A