We purified and characterized a thermophilic beta-galactosidase from Thermus sp. A4 isolated from the Atagawa hot spring (Shizuoka, Japan). The enzyme was monomeric, and its molecular mass was estimated to be 75 kDa by SDS-polyacrylamide gel electrophoresis. The enzyme was extremely thermostable and retained its full activity after incubation at 70 degrees C for 20 h. The Km observed were 5.9 mM for ortho-nitrophenyl beta-D-galactopyranoside and 19 mM for lactose. We cloned and analyzed the complete sequence of the gene encoding this enzyme. It was found to consist of 645 amino acid residues. We propose that this enzyme and seven other unclassified beta-galactosidases are new members of family 42 of the glycosyl hydrolases.

The bitter peptide fraction present in casein hydrolysates obtained by using three proteases (subtilisin, papain and trypsin) was treated with aminopeptidase T from 7'hennus aquaticus YT-1. The bitterness of the bitter peptide fraction could be decreased, and it sometimes disappeared completely, with an increase in free amino acids. The percentages of total free amino acids released from each bitter peptide fraction (subtilisin, papain and trypsin) by aminopeptidase digestion for 20 hr were approximately ll%, 8.7%, and 6.5%, respectively. Bitter peptide (a,l-CN f91-100) was isolated from a tryptic hydrolysate of casein by HPLC, its threshold value of bitterness being 2.9 ppm (w/v). The peptide (%l-CN f96-100) obtained from the amino peptidase digestion of this bitter peptide showed no bitterness.

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SummaryThe exopeptidase activities of five different strains of bifi dobacteria occurring habitually in healthy human intestinal canal were measured on 61 synthetic substrates. The cluster analysis, based on the results, indicates that four strains, with the exception of Bifidobacterium adolescentis a M101-4, have similar exopeptidase profiles. All CFE from these five strains contained at least three kinds of aminopeptidases (aminopeptidase with broad substrate specificity, amino peptidase hydrolyzing selectively X-Pro type and aminopeptidase hy drolyzing selectively Pro-X type) and carboxypeptidase.

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