Synthesis, characterization, and enzymic conversion of nonhydrolysable analogues of propionylcoenzyme A

We describe the synthesis of three novel analogues of propionyl-coenzyme A, in which the sulfur atom has been replaced by methylene, ethylene, and thiomethylene, respectively. All three analogues, propionyl-dethia(carba)-CoA (1), propionyl-dethia(dicarba)-CoA (2), and S-(2-oxobutanyl)-CoA (3) were characterized by 1H and 31P NMR spectroscopy and FAB mass spectrometry. Propionyl-CoA–oxaloacetate transcarboxylase from Propionibacterium shermanii accepted the novel analogues as substrates and carboxylated them to the corresponding methylmalonyl-CoA analogues (4–6). The latter were further converted into the succinyl-CoA analogues by the coenzyme-B12-dependent methylmalonyl-CoA mutase from the same organism. The succinyl-CoA analogues, succinyl-dethia(carba)-CoA (7), succinyl-dethia(dicarba)-CoA (8), and 4-carboxy(2-oxobutanyl)-CoA (9) were obtained on a preparative scale and their Michaelis constants (Km) with methylmalonyl-CoA mutase were determined to be 0.136, 2.20, and 0.132 mM, respectively (Km for succinyl-CoA is 0.025 mM). The Vmax values for 7, 8, and 9 are 1.1, 0.013, and 0.0047 µmol min−1 U−1, respectively (Vmax for succinyl CoA is 1.0). The utility of the novel coenzyme A analogues in enzyme mechanistic studies is discussed.