The action of tyrosinase on chymotrypsin, trypsin, and pepsin.

The action of the enzyme tyrosinase on proteins has recently been made the subject of a study by Sizer (1). He has claimed that among a variety of proteins tested those which contained tyrosine could be oxidized by tyrosinase either directly or after pretreatment with trypsin. The proteins most susceptible to the action of tyrosinase were said to be the proteolytic enzymes chymotrypsin, trypsin, and pepsin. Furthermore it was stated that the proteolytic activities of these enzymes were not decreased after the oxidation by tyrosinase of a certain part of the tyrosine residues, and the inference was drawn that the intactness of at least a part of the tyrosine residues was not essential for the action of the enzymes. This question has been reinvestigated in this laboratory as it seemed to us that for several reasons the experimental conditions used by Sizer did not permit an unequivocal interpretation.