Inhibition of proline endopeptidase activity by acyl-coenzyme A esters

Coenzyme A (CoA), its related compounds and acylcarnitine non-competitively inhibited the activity of proline endopeptidase (PEPase) purified from rat liver cytosol. The degree of inhibition was in the order of acyl-CoA greater than CoA greater than dephospho-CoA greater than or equal to acylcarnitine. However, carnitine did not inhibit the enzyme activity. Among the compounds examined, n-decanoyl-CoA showed the highest inhibitory activity (Ki = 9 microM). These results suggest that both the acyl group and CoA contribute to the inhibition of PEPase by acyl-CoA. The abilities of n-decanoyl-CoA and its related compounds to quench the intrinsic fluorescence at 332 nm from PEPase excited at 280 nm, was used as a probe for the binding affinity of the enzyme for these compounds. The quenching of fluorescence by CoA was nearly equal to that by n-decanoyl-CoA. n-Decanoylcarnitine and carnitine were unable to quench the fluorescence. These results indicate that n-decanoyl-CoA at least binds to PEPase through its CoA portion.