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Evidence for a Transcarboxylase Reaction in Maize Chloroplast Extracts

Pan, David, Tan, Kim H.
Zeitschrift für Naturforschung 2014 v.36 no.7-8 pp. 688-691
NAD (coenzyme), chloroplasts, corn, magnesium, malates, pH, pentoses, phosphates, thermal stability
The authors have suggested (Can. J. Bot. 49, 631 (1971) that the — COOH group of the C4-P carbonyl compound of the thermostable P-enolpyruvate acid carboxylase reaction may transcarboxylase with a pentose phosphate as ac­ ceptor. We now have considerable evidence supporting this consideration. In an assay system (0.8 ml) containing soni­ cated chloroplast extract in 0.1 m Tris-HCl, pH 6.3; and PEP, 0.1 |imol; Mg2+, 0.5 nmol; NADH, 0.25 nmol; sugar phosphate, 0.5 nmol. The amount of 14C 0 2 fixation is con­ siderably enhanced by either ribose-5-phosphate, fructose-1,6-bisphosphate or ribulose-l,5-bisphosphate in the pres­ ence of PEP. The products of the reaction include malate as a product of /?-carboxylation, and glycerate or 3-phosphate glycerate, their proportion being determined by the ac­ ceptor sugar phosphate. The results provide evidence for a "transcarboxylase" presented in the crude extract of Maize chloroplasts.