Isolation and Partial Characterization of Intracellular Proteinases in Lactococcus lactis ssp. lactis IAM 1198

¹ Department of Animal Products Science and Technology, Nippon Veterinary and Zootechnical College, Musashino-shi, Tokyo 180, Japan

Activities of intracellular proteinases of a strain of Lactococcus lactis were surveyed using a fluorometric method. The cell extract obtained upon disruption of harvested L. lactis cells, using a porcelain mortar and ultrasonic oscillation, was subjected to chromatography on a DEAE-cellulose column and then a Sephadex G-100 column. The eluates were assayed by a fluorometric method using benzyloxycarbonyl-L-phenylalanyl-L-arginine-7-(4-methyl) coumarylamide and casein as substrates. Four different caseinolytic fractions were obtained that were ascribable to two metalloproteinases of molecular weights 62,000 and 98,000; a serine proteinase of 160,000, and a cysteine proteinase of 12,000, respectively. Eight different benzyloxycarbonyl-L-phenylalanyl-L-arginine-7-(4-methyl) coumarylamide-hydrolyzing fractions were also obtained, three of which were attributable to cysteine proteinases with the molecular weights of 125,000, 125,000, and 300,000. None of the eight hydrolyzing fractions seemed to be able to hydrolyze casein.

Key Words: proteinase • Lactococcus lactis • cheese

Submitted on February 8, 1990
Accepted on June 4, 1990