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Localization of Proteinase(s) near the Cell Surface of Streptococcus lactis

^a New Zealand Dairy Research Institute, and Department of Microbiology and Genetics, Massey University, Palmerston North, New Zealand

ABSTRACT

Two criteria suggest that most of the proteinase of Streptococcus lactis is localized in the cell wall. (i) Intact cells possess proteinase activity when incubated with a high-molecular-weight substrate. (ii) Most of the cell-bound proteinase activity is released during spheroplast formation under conditions which result in the release of only 1% of the intracellular enzymes aldolase and glyceraldehyde-3-phosphate dehydrogenase. The solubilized cell wall, plasma membrane, and cytoplasm fractions contained 84, 0, and 16%, respectively, of the total proteinase activity with casein as substrate. The physiological role of a surface-bound proteinase in this organism is discussed.

¹ Present address: Department of Biology, McGill University, Montreal, Canada.