THERMAL-DENATURATION OF BETA-GALACTOSIDASE FROM STREPTOCOCCUS-THERMOPHILUS AND ITS STABILIZATION BY BOVINE SERUM-ALBUMIN - AN ELECTROPHORETIC STUDY

The thermal denaturation of beta-galactosidase from Streptococcus ther mophilus was monitored by electrophoresis of samples of native and hea ted enzyme. The native enzyme (N1) was primarily in the form of a tetr amer (molecular mass 430 kDa), but some active dimer (D4) was also pre sent in all samples. Heating at 60 degrees C caused the appearance of a new dimer (D3), which was the last active species observed before ag gregation and loss of activity. It is proposed that the denaturation f ollows the scheme: tetramer-->dimer D4-->dimer D3-->aggregates. Dissoc iation of the tetramer was slowed in the presence of lactose, which st abilized the enzyme. Stability was further enhanced by the addition of BSA, which bound to the D4 dimer. It is therefore proposed that the f ormation of the dimer-BSA complex is responsible for the stabilization of the enzyme by BSA.