Oct 25, 1976

Studies on the regulation of chloroplast NADP-linked glyceraldehyde-3-phosphate dehydrogenase

The Journal of Biological Chemistry
R A Wolosiuk, B B Buchanan

Abstract

Chloroplast NADP-linked glyceraldehyde-3-phosphate dehydrogenase was resolved into three forms that differed in molecular weight: (a) larger than or equal to 1.5 million; (b) 600,000; and (c) less than or equal to 100,000. After preincubation with an effector (ATP, NADPH, or Pi) the activity of forms a and c was unaffected, whereas the activity of b, the regulatory form, was increased 10-fold. Activation was accompanied by the exposure of previously hidden sulfhydryl groups. The rate of activation was slower than the rate of catalysis and resulted in a lag phase during the measurement of activity when the enzyme was preincubated in the absence of an effector. The addition of one of several compounds as a second effector (at a concentration which itself was nonactivating) in the presence of a first effector enhanced activation by lowering the concentration of the first effector required for half-maximal activation (Pi constant/ATP or NADPH varied; ATP or NADPH constant/Pi varied). Other combinations of effectors caused little change in activity (ATP constant/NADPH varied; NADPH constant/ATP varied). Glyceraldehyde 3-phosphate added as a second effector induced contrasting changes: an increase in the ATP-mediated activation and a...Continue Reading

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Mentioned in this Paper

GAPDH gene
Sulfhydryl Compounds
Chloroplasts
Contrast Used
NADP
Etioplasts
Glyceraldehyde-3-phosphate dehydrogenase
Glyceraldehyde-3-Phosphate Dehydrogenases
Metabolite
Orthophosphate

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