The alpha-galactosidase gene of Streptomyces coelicolor A3(2) was cloned, expressed in Escherichia coli and characterized. It consisted of 1497 nucleotides encoding a protein of 499 amino acids with a predicted molecular weight of 57,385. The observed homology between the deduced amino acid sequences of the enzyme and alpha-galactosidase from Thermus thermophilus was over 40%. The alpha-galactosidase gene was assigned to family 36 of the glycosyl hydrolases. The enzyme purified from recombinant E. coli showed optimal activity at 40 degrees C and pH 7. The enzyme hydrolyzed p-nitrophenyl-alpha-D -galactopyroside, raffinose, stachyose but not melibiose and galactomanno-oligosaccharides, indicating that this enzyme recognizes not only the galactose moiety but also other substrates.

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An a-galactosidase gene belonging to glycoside hydrolase family ,1 from Streptomyces coelicolor was cloned and expressed in E. coli. The purified enzyme showed a single protein band on SDS-PAGE with a molecular mass of 0. kDa. It was quite stable from pH /.* to +*.* after treatment at .*ῌ for 0* min, and was thermally stable up to /*ῌ. The enzyme acted on galacto-oligosaccharides, galactomanno-oligosaccharides and galactomannans as well as plant a-galactosidases. It consisted of an N-terminal catalytic domain (.** amino acid residues) and a C-terminal region (,0* amino acid residues). The catalytic domain of the enzyme was constructed by deleting the C-terminal region from the enzyme and was found to be stable from pH /./ to 2./ and up to .*ῌ. The catalytic domain showed the same specificity towards galactooligosaccharides, galactomanno-oligosaccharides and galactomannans as the enzyme containing the Cterminal region. These results indicated that the C-terminal region probably has an important role in stabilizing the enzyme.

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