Hysteretic Properties of NADP-malic Enzyme from Sugarcane Leaves

A.A. IGLESIAS, C.S. ANDREO

PHOTOSYNTHESIS RESEARCH

Año: 1992 vol. 31 p. 89 - 97

0166-8595

Alberto A. Iglesias1, 2   and Carlos S. Andreo1, 2 (1)  Centro de Estudios Fotosintéticos y Bioquímicos Consejo Nacional de Investigaciones Científicas y Técnicas, Fundación Miguel Lillo, Suipacha 531, 2000 Rosario, Argentina (2)  Universidad Nacional de Rosario, Suipacha 531, 2000 Rosario, Argentina (3)  Dr. Alberto A. Iglesias, Department of Biochemistry, Biochemistry Building, Michigan State University, 48824 East Lansing, MI, USA Received: 9 September 1991  Accepted: 4 October 1991   Abstract  NADP-malic enzyme highly purified from sugarcane leaves exhibited hysteretic properties. This behavior resulted in a lag phase during activity measurement of the enzyme preincubated in the absence of substrates. The lag was inversely proportional to the protein concentration during preincubation, which suggests that changes in the aggregational state of the enzyme are responsible for hysteresis. The pH conditions as well as the presence of different compounds in the preincubation medium modified the hysteretic properties of the enzyme. Mg2+ eliminated the lag period and increased the enzyme activity by nearly 2-fold. NADP+, 3-phosphoglycerate, ATP and dithiothreitol shortened the lag phase. The substrate l-malate inhibited the enzyme by decreasing the steady state velocity and increasing the lag time in a concentration-dependent manner. NADPH, triose-phosphates and high ionic strength increased the lag phase. Results are consistent with the view that the level of different metabolites and the pH conditions at the chloroplast regulate the activity of NADP-malic enzyme in a coordinate and effective manner.