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  • Title: Photoreductive path of carbon fixation in green plant photosynthesis. Reaction pathway of six-carbon ribulose 1,5-bisphosphate carboxylation adduct intermediate.
    Author: Fong FK, Butcher KA.
    Journal: Biochem Biophys Res Commun; 1987 Feb 13; 142(3):732-7. PubMed ID: 3827899.
    Abstract:
    In this paper we examine the six-carbon intermediate pathway of ribulose 1,5-bisphosphate (RuBP) carboxylation reaction in photosynthesis. Based on the observed reactions of purified RuBP carboxylase, mechanisms are described for carbon dioxide assimilation leading to the hydrolytic splitting of the six-carbon intermediate to two enzyme-bound glycerate-3-P (3-PGA) molecules. It is concluded that, under photosynthetic conditions, the reduction of enzyme-bound NADP+ by the chlorophyll is responsible for the rapid carboxylase turnover rate given by the lifetime, tau L = 0.4 s, which is nearly two orders of magnitude shorter than the corresponding value, tau D = 11 +/- 3 s, for the dark decay of enzyme-bound RuBP. The nocturnal inhibition and photoactivation of RuBP carboxylation are described in terms of the reversible light-dark cycles of the NADP+/NADPH redox couple and endogenous changes that accompany the 2-carboxy-D-arabinitol-1-phosphate binding to the enzyme active site.
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