MODIFICATION OF BOVINE PANCREATIC RIBONUCLEASE A WITH PYRIDOXAL 5‘-PHOSPHATE. ISOLATION AND IDENTIFICATION OF DERIVATIVES

Bovine pancreatic ribonuclease A was allowed to react with pyridoxal 5′-phosphate at pH 8 and 4°. After reduction with sodium borohydride, the principal products formed in the initial stages of modification were separated by successive chromatography on CM-cellulose and SP-Sephadex. The isolated derivatives were identified as Nα-(P-pyridoxyl)-Lys-1-, Ne-(P-pyridoxyl)-Lys-7-, and Ne-(P-pyridoxyl)-Lys-41-ribonuclease A. These results are interpreted in terms of the specificity of pyridoxal-P as a protein reagent.