(I) Inorganic components . . . . . . . (a) Nitrate . . . . . . . . . (b) Cation-anionuptake . . . . . . (2) Organic compounds . . . . . . . (a) Amino acids and other organic nitrogenous compounds (b) Organic acids . . . . . . . . (3) Effects on flowering . . . . . . . (4) Ammonium plus nitrate as a nitrogen source . . . ( 5 ) Metabolic changes characteristic of ammonium toxicity . VII . Summary . . . . . . . . . . VI . Physiological effects of nitrogen sources . . . .

Ammonium and nitrate nutrition of plants

Ribulose-1,5-bisphosphate carboxylase was activated by incubation with CO2 and Mg2++, and inactivated upon removal of CO2 and Mg2+ by gel filtration. The activation process involved CO2 rather than HCO3-. The activity of the enzyme was dependent upon the preincubation concentrations of CO2 and Mg2+ and upon the preincubation pH, indicating that activation involved the reversible formation of an equilibrium complex of enzyme-CO2-Mg. The initial rate of activation was linearly dependent upon the CO2 concentration but independent of the Mg2+ concentration. Kinetic analyses indicated that the enzyme reacted first with CO2 in a rate-determining and reversible step, followed by a rapid reaction with Mg2+ to form an active ternary complex (see eq 1 in text). The pseudo-first order rate constant, kobsd, for the activation process at constant pH was derived: kobsd=k1[CO2] + (k2k4/k3[Mg2+]). Experimentally, kobsd was shown to be linearly dependent upon the CO2 concentration and inversely dependent upon the Mg2+ concentration. The activity of the enzyme after preincubation to equilibrium at constant concentrations of CO2 and Mg2+ increased as the preincubation pH was raised, indicating that CO2 reacted with an enzyme group whose pK was distinctly alkaline. It is proposed that the activation of ribulose-1, 5-biphosphate carboxylane involves the formation of a carbamate.

The activation of ribulose-1,5-bisphosphate carboxylase by carbon dioxide and magnesium ions. Equilibria, kinetics, a suggested mechanism, and physiological implications.

Mitochondria and glyoxysomes from castor bean endosperm. Enzyme constitutents and catalytic capacity.

Exogenous inorganic carbon sources in plant photosynthesis

Effect of carbon dioxide on yeast growth and fermentation

The Carboxylation of Phosphoenolpyruvate and Pyruvate I. THE ACTIVE SPECIES OF "CO2" UTILIZED BY PHOSPHOENOLPYRUVATE CARBOXYKINASE, CARBOXYTRANSPHOSPHORYLASE, AND PYRUVATE CARBOXYLASE

T. T. Tchen

Papers

The Carboxylation of Phosphoenolpyruvate and Pyruvate I. THE ACTIVE SPECIES OF "CO2" UTILIZED BY PHOSPHOENOLPYRUVATE CARBOXYKINASE, CARBOXYTRANSPHOSPHORYLASE, AND PYRUVATE CARBOXYLASE

The Species of "CO 2 " Utilized in the Carboxylation of P-Enolpyruvate and Pyruvate