title: The suicide inactivation of ox liver short-chain acyl-CoA dehydrogenase by propionyl-CoA. Formation of an FAD adduct.
abstract: Propionyl-CoA gave an unexpectedly low turnover (0.03 s-1) and high Km (153 microM) as a substrate for ox liver short-chain acyl-CoA dehydrogenase (SCAD). On addition of an excess of propionyl-CoA to SCAD the flavin A448 decreased to about 30% of its original value and the peak at 368 nm was replaced by one at 335 nm. The decrease in A448 exhibited first-order kinetics and correlated with a first-order decrease in the enzyme's catalytic activity to 22% of the initial value. The flavin, released from propionyl-CoA-treated enzyme with trichloroacetic acid, reacted with O2 to form a stable free radical. This suggests that a reduced N-5 flavin adduct is formed on the enzyme and protected from O2. The released adduct was separated from unmodified flavin and excess propionyl-CoA by h.p.l.c., and was shown by 3H-labelling to contain CoA. The incompleteness of the decrease in the enzyme's A448 and specific activity on incubation with propionyl-CoA probably reflects an equilibrium between covalently and non-covalently bound acyl-CoA, since the spectral changes could be reversed. The enzyme was also re-activated by dilution and incubation with a large molar excess of butyryl-CoA. The rate constant, approx. 2 X 10(-3) s-1, for re-activation, taken with the extrapolated rate constant for the opposing inactivation reaction, 8.9 X 10(-3) s-1, explains the 22% residual activity at equilibrium. The results suggest that propionyl-CoA is a suicide inhibitor for SCAD.
mesh_terms: D000214:Acyl Coenzyme A / Q000494:pharmacology*; D042964:Acyl-CoA Dehydrogenase; D044944:Acyl-CoA Dehydrogenases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D004789:Enzyme Activation; D005182:Flavin-Adenine Dinucleotide / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D010084:Oxidation-Reduction; D013053:Spectrophotometry
chemical_list: D000214:Acyl Coenzyme A; D005182:Flavin-Adenine Dinucleotide; C009061:propionyl-coenzyme A; D044944:Acyl-CoA Dehydrogenases; D042964:Acyl-CoA Dehydrogenase