Steps in the formation of active derivatives of staphylococcal nuclease during trypsin digestion.

A staphylococcal nuclease (strain Foggi), very similar in chemical structure to the enzyme from strain V8, is cleaved in a limited way by trypsin in the presence of deoxythymidined/,5’-diphosphate and Ca++. Such treatment yields fragments PI (residues 1 to 5), PZ (residues 6 to 48), P3 (Psa, residues 49 to 149; and P3b, 50 to 149), and free lysine (residue 49). None of the products shows enzymatic activity. However, Fragments Pf and PB (either Paa or P& associate to form an active, noncovalently bonded derivative, nuclease-T. Evidence is presented to show that the cleavage of the peptide bonds in nuclease between residues 48 and 49 or between 49 and 50, but not the bond between residues 5 and 6, account for the decreased enzymatic activity and heat stability observed with nuclease-T.