LIMITED PROTEOLYSIS OF CHLOROPLAST GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE (NADP) FROM SPINACIA-OLERACEA

The structural and functional properties of chloroplast glyceraldehyde -3-P-dehydrogenase I (D-Glyceraldehyde-3-phosphate: NADP oxidoreductas e (phosphorylating) EC 1.2.1.13) from Spinacia oleracea were investiga ted by limited proteolysis. The enzyme is insensitive to trypsin and c hymotrypsin, while Staphylococcus aureus V8 protease cleaves the C-ter minal region of its subunits. Subunit A (36 kDa) is only partially cle aved at Glu 317. No intact subunit B (39 kDa) is found at the end of t he proteolytic experiment: two forms are originated from this subunit which is cleaved at Glu 342 and Glu 320. Proteolytic cleavage at these sites does not significantly alter enzymatic activity, but leads to d estabilization of the protein. Unlike the intact parent enzyme (600 kD a) the cleaved enzyme behaves as a 150-kDa species in size exclusion c hromatography.