2 HISTIDINES ARE ESSENTIAL FOR THE ACTIVITY OF THE BETA-GALACTOSIDASEFROM LACTOBACILLUS-DELBRUCKII SUBSP BULGARICUS

Twelve tyrosines, ten glutamates, and five histidines were individuall y substituted for phenylalanine, glutamine, and asparagine, respective ly, in the beta-galactosidase from Lactobacillus delbruckii subsp. bul garicus. Only Y509, E464, H351, and H534 appear to be essential for th e activity of the enzyme. The residues Y509 and E464 are homologous to Y503 and E461, respectively, of the Escherichia coli lacZ beta-galact osidase which have been shown to be necessary for its activity. Surpri singly, a number of amino acids that are highly conserved in the seque nce alignments of nine beta-galactosidases and four beta-glucuronidase s are not essential for enzyme activity. (C) 1994 Academic Press, Inc.