A. Semenihina et al., Purification and some catalytic properties of glucose-6-phosphate dehydrogenase isoforms from barley leaves, PHOTOSYNTHE, 39(2), 2001, pp. 299-304
The cytosolic and chloroplastic isoforms of glucose-6-phosphate dehydrogena
se (G(6)PDH) were separated and purified from barley leaves (Hordeum vulgar
e L.). In etiolated leaves, only the cytosolic isoform was expressed. The m
olecular mass of the cytosolic enzyme, G(6)PDH(1), was 112 +/-8 kDa and tha
t of the chloroplast enzyme, G(6)PDH(2), was 136 +/-7 kDa. The K-m values f
or glucose-6-phosphate and NADP were 0.133 and 0.041 mM for G(6)PDH(1), and
0.275 and 0.062 mM for G(6)PDH(2), respectively. The pH optimum was 8.2 fo
r G(6)PDH(1) and 7.8 for G(6)PDH(2). The enzyme is absolutely specific for
NADP. NADPH is a competitive inhibitor of the G(6)PDH(1) in respect to gluc
ose-6-phosphate (G(6)P) and NADP (K-i = 0.050 and 0.025 mM, respectively).
NADPH is a competitive inhibitor of the G(6)PDH(2) in respect to NADP (K-i
= 0.010 mM), but a non-competitive inhibitor in respect to the G(6)P. ADP,
AW, UTP, NAD, and NADH had no effect on the activity of G(6)PDH. ATP inhibi
ted the G(6)PDH(2) activity.