Fig. (4) Catalase activity (U/mg) of pigmented (red) and unpigmented (white) Serratia marcescens cell lysates, normalized to protein concentrations. Heating of lysates to 50°C did not affect catalase activity, but activity was significantly lower in lysates heated to 75°C or 100°C (P < 0.05). For temperature stability assays, only cell lysates were used.