3-PHOSPHO-D-GLYCERATE CARBOXYLYASE[DIMERIZING]

D-Ribulose 1,5-Diphosphate Carboxylase from spinach has been used:

• as a test protein in pepsin digestion studies
• as an innocuous or non-hazardous protein sample to test its effect on human intestinal epithelial cell lines
• in isothermal titration calorimetry (ITC), and radiolabeled binding assays with abscisic acid

Exists as a 557?kDa hexadecamer composed of eight heavy chains each with a molecular weight of approximately 56?kDa and eight light chains of molecular weight 14?kDa. Each molecule contains one magnesium ion.
pH optimum: ~7.9.
K_M for CO₂: ~0.45 mM.
Ribulose diphosphate becomes inhibitory at concentrations exceeding 0.7 mM. Orthophosphate and ammonium sulfate are competitive inhibitors. 3-Phosphoglycerate is a noncompetitive inhibitor.

D-Ribulose 1,5-Diphosphate Carboxylase (RUBISCO) depends on Rubisco activase and chaperones for activation. It participates in plant photorespiration events by catalyzing the carboxylation and oxygenation of ribulose-1,5-bisphosphate. Abscisic acid inhibits the carboxylation activity of Rubisco.