In vitro and in vivo regulation of chloroplast glyceraldehyde‐3‐phosphate dehydrogenase isozymes from Chenopodium rubrum. II. In vitro modulation of the isozyme pattern

Abstract

Isozymes of chloroplast glyceraldehyde‐3‐phosphate dehydrogenase (GPD, EC 1.2.1.13) from Chenopodium rubrum were separated using inverse discontinuous ammonium sulphate gradient solubilization. Leaves were extracted at the 9th h of light and the 9th h of darkness of a 12 h light/12 h dark cycle. The ratio of “NADP‐GPD I” to “NADP‐GPD II” varied with the light/dark cycle. However, the “light” isozyme pattern could be obtained from “dark” plants by including NADP + or NAD + kinase in the extraction buffer. Similarly, the “dark” isozyme pattern was produced in “light” plants extracted in the presence of NAD+. Pyridine nucleotides had no effect on the separated, purified isozymes. It is concluded that differential binding of the isozymes at the moment of extraction to pelletable material in the crude extract determines the isozyme pattern, and that this binding is regulated by the pyridine nucleotide ratio.

Enzyme patterns in energy metabolism during flower induction in spinach leaves

“…In SD, the chloroplastic NADP-GPD capacity is increased by the light-on signal for 2 h, then it decreases continuously up to midnight. The NAD-GPD capacity, which represents the sum of cytoplasmic and chloroplastic isozymcs (De Looze & Wagner, 1983b), is decreased by the light-on and light-off signals. Its capacity is characterized by three peaks: at noon, at midnight and at the vety end of the night NADP-GPD span.…”

“…Only three enzymes have their capacities increased during the night: NAD-GPD and 6-PGDH peak at tnidnight, and MDH at the end of the night span. The reciprocally-phased oscillations in NAD-and NADP-GPDs, which have already been observed by Myiata & Yatnatnoto (1969), Frosch etal., (1973, Walther & Edtnunds (1973), Goto (1978) and De Jong & Woodlief (1979), suggest the existence of an endogenous rhythm synchronized by the light-oti signal (Frosch et al, 1973), It would be teti-ipting to interpret this fact as reciprocal changes in the glycolytic space and in chloroplasts but this could as well be accounted for by the tnodulation of the chloroplast isozyrne pattern by pyridine nucleotides (De Looze & Wagner, 1983b), Indeed, it should be pointed out that the pool size changes in adenine and pyridine nucleotides tneasured in crude extracts by Bonzon etal. (1981Bonzon etal.…”