α-Methylacyl-CoA racemase (AMACR; P504S) catalysed exchange of straight-chain fatty acyl-CoA α-protons. One α-proton was removed in each catalytic cycle, with the pro-S proton preferred. This reaction was most efficient for straight-chain substrates with longer side-chains. 2-Methyldecanoyl-CoA underwent α-proton exchange 3× more efficiently (as judged by Kcat/Km) than decanoyl-CoA.