Purification and thermostability of beta-galactosidase (lactase) from an autolytic strain of Streptococcus salivarius subsp. thermophilus.
beta-Galactosidase from an autolytic strain of Streptococcus salivarius subsp. thermophilus was purified 109-fold to near homogeneity. The yield of purified enzyme was 41% and the specific activity was 592 o-nitrophenyl beta-D-galactopyranoside U/mg at 37 degrees C. Two isozymes were present, but only one subunit was detected, having a mol. wt of 116,000. Enzyme stability was 37-83 times greater in milk than in buffer in the range 60-65 degrees C. At 60 degrees C the half-life in milk was 146 min. Denaturation in buffer was first-order, but in milk the overall reaction order with respect to enzyme concentration was approximately 0.5. The activation energy for denaturation was 453 kJ/mol in milk and 372 kJ/mol in buffer. In milk the activation energy for lactose hydrolysis was 35.1 kJ/mol.
Chang
B S
BS
Department of Food Science and Nutrition, University of Massachusetts, Amherst 01003.
Mahoney
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RR
D000818:Animals; D004795:Enzyme Stability; D005696:Galactosidases / Q000302:isolation & purification*; D006358:Hot Temperature; D008892:Milk / Q000201:enzymology; D013291:Streptococcus / Q000201:enzymology*; D001616:beta-Galactosidase / Q000032:analysis / Q000302:isolation & purification*
D005696:Galactosidases; D001616:beta-Galactosidase