A Comparative Study: Aminopeptidase Activities from Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus

¹ Laboratory of Dairy Research, Agricultural University of Athens, 118 55 Athens, Greece

Aminopeptidases from Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus were isolated. Enzymes were purified by chromatography on DEAE-cellulose and Sephadex G-150. The enzymes had molecular weights of 98,000 and 89,000 and optimal activity at pH 6.0 and 40°C and pH 6.5 and 35°C. respectively. The L. delbrueckii ssp. bulgaricus enzyme had higher activity on L-lysyl-4-nitroanilide than did the S. thermophilus enzyme. Both enzymes were inactivated by EDTA and 1,10-phenanthroline. Classical sulfhydryl and serine group reagents had little or no inhibitory effect on the enzymes; nevertheless, Cu⁺⁺ and Hg⁺⁺ resulted in strong inhibition; Ca⁺⁺ stimulated the L. delbrueckii ssp. bulgaricus enzyme, and Mg⁺⁺ stimulated the S. thermophilus enzyme.

Key Words: aminopeptidase • Lactobacillus • delbrueckii ssp. bulgaricus • Streptococcus thennophilus

Submitted on July 27, 1992
Accepted on February 19, 1993

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