Evidence for multiple pairs of vicinal thiols in some proteins.

The oxidizing agent periodate has been used as an analogue of phosphate. The reaction of periodate with some enzymes which have a phosphate-binding site causes only the formation of disulfide bridges and the loss of the catalytic activity. Phosphate and other tetrahedral anions protect against inactivation. Other enzymes are not inactivated by periodate, which seems to be specific for vicinal thiols. The results obtained suggest (a) the use of periodate for the detection of vicinal thiols in proteins, (b) the presence of multiple pairs of vicinal thiols in the proteins tested, and (c) the presence of these pairs at a phosphate-binding site. An hypothesis on the chemical structure of the phosphate-binding site of some proteins is advanced.