Abstract:Primary study of NAD-malic enzyme was carried out in facultative CAM plants Sedum aizoon and Mesembryanthemum cordifolium. When 5 mmol/L MnC12, 6 mmol/L Mal and 50μmol/L CoA are present, the optimum pH is 7. The activity of this enzyme fluctuates with the seasons, in July, its activity reaches the summit. Its activity has a diurnal change also, being higher during the day and lower during the night. After water stress, the activity of this enzyme increases 2—3 times. The authors consider that the CAM activity may be regulated by carboxylate and decarboxylate system together.