1H‐n.m.r. studies on cross‐relaxation phenomena in bovine mercaptalbumin (BMA) solution and partially hydrolyzed bovine plasma albumin (BPA*) gel

Bovine plasma albumin Fr. V(BPA) contains small amounts of proteolytic enzyme which catalyzes a very limited cleavage of 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 7%. Highly purified proteolytic enzyme‐free bovine mercaptalbumin (BMA) was in a transparent solution at pD 4.0 even at 12.4%. after 5 days incubation at 35°. Cross‐relaxation times (TIS) between irradiated protein protons and observed protons, such as side chain and water protons, were studied on BMA solution and BPA*‐gel. TIS values of BMA solution, obtained by the saturation transfer (SATUR) and inversion recovery (INVER) methods, were a single kind of TIS for each side chain. Those of BPA*‐gel by the SATUR method indicated the presence of two kinds of TIS, that is, short and long TIS values for each side chain. However, those by the INVER method showed a single kind of TIS for each side chain, corresponding to the long TIS value by the SATUR method. The short TIS values of BPA*‐gel, observed by the SATUR method, may be due to immobile joint parts of fibrous BPA* aggregates. TIS values from protein to water protons (TIS(HDO)) in BPA*‐gel, obtained by the INVER method, were far shorter than those in BMA solution, indicating a large amount of hydration of BPA* and rapid exchange between bound and bulk water in the gel state.