A phospholipid-deacylating system of bacteria active in a frozen medium

A phosphatidylcholine-deacylating system present in a Butyrivibrio species (probably fibrisolvens) shows appreciable activity at low temperatures with a maximum hydrolysis rate at--10 degrees C. 2. The rate at--10 degrees C is higher than at 39 degrees C unless the system at the latter temperature is stimulated by adding oleic acid or sodium dodecyl sulphate. 3. The low-temperature phospholipase activity has an absolute requirement for thiol reagents, e.g. cysteine, dithiothreitol or mercaptoethanol. 4. Ca2+, Mg2+ and Mn2+ stimulate the activity up to 10 mM, but EDTA inhibits; higher concentrations of Ca2+ also inhibit. 5. The enhancement of activity at low temperatures appears not to be associated with a crystalline change in the hydrated phospholipid substrate, but depends on the formation of a solid phase in the incubation medium which brings the substrate and bacterial cells into juxtaposition or causes fusion.