Abstract: A variety of factors were comparatively studied with regard to their effects on the stability of phosphoglucomutase (PGM)in Chinese cabbage.It was clearly shown that PO43-was most effective in maintaining the enzyme activity, while Tris-Cl was most ineffective.Inclusion of such possible enzyme protectants as DTT, PMSF, glucose and Mg in phosphate extraction buffer did not improve PGM stability any furthur.It was also shown that PGM enzyme was much affected by pH change, with low pH harmful and pH8.0 optimal.For these reasons, pH8.0 phosphate buffer was used throughout the process of PGM purification.The three PGM isozymes were successfully separated from the etiolated seedlings of Chinese cabbage “Baiyang”, by a series of methods from extraction, stepwise ammonium sulphate precipitation, Sephadex G75 chromatography and finally DEAE-cellulose HPLC.The Michaelis constants (Km) of these two isozymes (one is the heat-tolerance related PGM)were then determined, and their heat stability was evaluated directly by incubation at 37℃.No essential differences were found between them, indicating that the observed heat-tolerance of Chinese cabbage cannot be attributed to any individual PGM isozyme.

Key words: Phosphoglucomutase, Isozyme, Michaelis constants, Heat-tolerance, Chromatography, Chinese cabbage