Water structure in modified bovine plasma albumin (BPA*) gel and bovine mercaptalbumin solution† 1 H‐n.m.r. studies

Bovine plasma albumin Fr. V (BPA) has been known to contain small amounts of proteolytic enzyme. Wilson & Foster (1971) found a very limited and specific cleavage of BPA catalyzed by the enzyme with BPA in the F‐form near pH 3.8, resulting in the formation of partially hydrolyzed BPA (BPA*). BPA* had a tendency to form a transparent gel at pD 4.0 (pD range of the F‐form) above 8%, though proteolytic enzyme‐free bovine mercaptalbumin (BMA) was in a transparent solution at pD 4.0 even at 12%. Water structures of the F‐form of BMA in the solution state and of BPA* in the gel state were studied by measuring 1 H‐n.m.r. spectra, spin‐lattice relaxation time (T1) and cross relaxation time (TIS) between irradiated and observed protons. Protein concentration‐dependent changes of T1 of water protons indicated that the amount of hydrated water of BPA* in the gel state is far greater than that of the F‐form of BMA in the solution state. TIS values from protein protons to water protons also indicated a large amount of hydration of BPA*, strong interaction between water and BPA* and rapid exchange between bound and bulk water in the gel state.