SHORT DIGESTION OF BOVINE SERUM ALBUMIN WITH PEPSIN. ISOLATION AND CHARACTERIZATION OF FRAGMENTS AND THEIR LOCATION IN THE ALBUMIN MOLECULE

After short peptic digestion of bovine serum albumin between pH 3.6 and 3.9, a limited number of well defined fragments are found. The isolation and characterization of some fragments, probably placed in the C‐terminal part of albumin, have been given in a previous paper. This paper describes the isolation, characterization and localization of a number of N‐terminal fragments of bovine serum albumin. The investigation comprises molecular weight determination, amino acid analysis, N‐terminal amino acid determination, copper binding studies and SH‐group determination. It is concluded that cleavage of albumin by pepsin between pH 3.6 and 3.9 preferentially occurs in the C‐terminal moiety of albumin. This leads to the appearance of large fragments with the same N‐terminal end as albumin. The mechanism of the digestion by pepsin is discussed in relation to the structural model of albumin and the conformational change at low pH (N‐F transition).