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>Mechanism of control by a circadian oscillator of chloroplast NADP-linked glyceraldehyde 3-phosphate dehydrogenase inLemna gibbaG3
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Mechanism of control by a circadian oscillator of chloroplast NADP-linked glyceraldehyde 3-phosphate dehydrogenase inLemna gibbaG3
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机译：Mechanism of control by a circadian oscillator of chloroplast NADP-linked glyceraldehyde 3-phosphate dehydrogenase inLemna gibbaG3
The mechanism controlling diurnal change in apparent Kmfor NADP of Chl- NADP-GPD ofLemna gibbaG3 in continuous light was studied. This enzyme included two molecular species (Chl-NADP-GPD I and II) which were both bifunctional, i.e., NADP- and NAD-linked. Apparently, Chl-NADP-GPD I was an allosteric enzyme with a molecular weight of ca. 520,000 and a low affinity for NADP, whereas Chl- NADP-GPD II was a non-allosteric enzyme with a molecular weight of ca. 170,000 and a high affinity for NADP. In vitro, Chl-NADP-GPD I was dissociated to Chl-NADPGPD II and a yet unidentified binding factor upon addition of DTT, ATP or NADP(H), while in their absence, Chl-NADP-GPD II associated with the binding factor to form Chl-NADP-GPD I. On the other hand, Vmaxfor NADP of Chl-NADP-GPD I (or II) in vivo decreased (or increased) in the subjective day phase of a day and increased (or decreased) in the subjective night phase. It was concluded that the decrease in Kmof Chl-NADP-GPD in L.gibbaG3 in the subjective day (4) could be ascribed to the promoted dissociation of Chl-NADP-GPD I due to an increased level of some DTT-like compound(s) and/or NADP(H), or to a decrease of NAD(H) and/or the binding factor, and that the increase in Km in the subjective night (4) could be ascribed to promoted association of Chl-NADP-GPD II with the binding factor due to a decrease in the amount of DTT-like compound(s) and/or NADP(H), or to an increase in NAD(H) and/or the binding factor.
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