Treatment with diallyl disulfide, a constituent of garlic oil, irreversibly inactivated microsomal and a soluble 50 kDa form of HMG-CoA reductase. No radioactivity was found to be protein-bound on treating the soluble enzyme with [35S]diallyl disulfide, indicating the absence of the mixed disulfide of the type allyl-S-S-protein. SDS-PAGE and Western blot analyses of the diallyl-disulfide-treated protein showed no traces of the dimer of the type protein-S-S-protein, but clearly indicated BME-reversible increased mobility, as expected of an intramolecular protein disulfide. The sulfhydryl groups, as measured by alkylation with iodo[2-14C]acetic acid, were found to decrease in the diallyl-disulfide-treated enzyme protein. Tryptic peptide analysis also gave support for the possible presence of disulfide-containing peptides in such a protein. It appears that diallyl disulfide inactivated HMG-CoA reductase by forming an internal protein disulfide that became inaccessible for reduction by DTT, and thereby retaining the inactive state of the enzyme.
R. V. Omkumar, Kadam, S. M., Banerji, A., and Ramasarma, T., “On the involvement of intramolecular protein disulfide in the irreversible inactivation of 3-hydroxy-3-methylglutaryl-CoA reductase by diallyl disulfide”, Biochimica et Biophysica Acta (BBA)-Protein Structure and Molecular Enzymology, vol. 1164, pp. 108–112, 1993.