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Carbohydrate Metabolism of Lactic Acid Cultures.^{1, 2,} II. Different Pathways of Lactose Metabolism of Streptococcus lactis and Their Sensitivity to Antibiotics

Department of Food Science and Technology, University of Nebraska, Lincoln

ABSTRACT

Enzymic studies of lactose catabolism of Streptococcus lactis UN revealed that the organism possessed lactase or ß-galactosidase, and lactose dehydrogenase activities. The organism did not exhibit lactose phosphorylase activity, and it did not show that lactose-1-phosphate was an intermediate in the metabolism of lactose. S. lactis utilizes lactose by possibly two pathways: a) by hydrolytic cleavage of lactose to glucose and galactose, effected by lactase or ß-galactosidase, and b) by oxidation via lactose dehydrogenase to lactobionate, before its enzymatic cleavage to gluconate and galactose. Penicillin, streptomycin, aureomycin, and terramycin inhibited the activity as well as the production of enzyme systems associated with lactose catabolism. The hydrolytie enzymes were inhibited mildly; whereas, lactose dehydrogenase was inhibited very markedly.

¹ Supported in part by U.S. Public Health Service Research Grant E-2486, from the National Institute of Allergy and Infectious Diseases.

² Published with the approval of the Director as paper no. 1756, Journal Series, Nebraska Agricultural Experiment Station, Lincoln.