The Effect of Zinc on the Formation of Ribulose Diphosphate Carboxylase in Phaseolus vulgaris

The effect of Zn on the formation of ribulose diphosphate carboxylase (RuDPCase was investigated in the leaf discs from Zn-deficient Sanilac navy bean plants (Phaseolus rulgaris L.). The incorporation of ¹⁴C-leucine into the partially purified RuDPCase was found to be a quantitative equivalent of the level and activity of the enzyme. Zn as ZnSO₄ at 10 uM stimulates the formation of RuDPCase by at least 2-fold. Neither CuSO₄ nor CdSO₄ at the same concentration substitutes for ZnSO₄. The enhancement of RuDPCase formation by added Zn is greater with increasing severity of Zn deficiency, suggesting that Zn is a limiting factor in this system. Suppression of the Zn-stimulated formation of RuDPCase by actinomycin D and cycloheximide suggests that the Zn-mediated formation of RuDPCase most likely represents de novo synthesis. Also, the possible site(s) of action of Zn is discussed.