Mechanism of the hexamer-dodecamer reaction of lobster hemocyanin.
The overall forward and reverse rate constants for the hexamer-dodecamer reaction of lobster hemocyanin have been determined in 0.1 ionic strength glycine buffers at pH 9.6, at free calcium ion levels from 0.0031 to 0.0053 molar, at 25 degrees C. Concentration-jump relaxation experiments in a stopped-flow apparatus were monitored by light scattered at 90 degrees. The reaction is pseudobimolecular, and the overall forward rate constant bears virtually all of the calcium ion concentration-dependence, while the overall reverse rate constant is truly unimolecular. Four calcium ions appear to participate in the reaction between two hexameric molecules, and appear to become an integral part of the structure of the dodecameric molecule under these conditions.
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000032:analysis; D006433:Hemocyanins / Q000032:analysis; D007700:Kinetics; D008024:Ligands; D046911:Macromolecular Substances; D008433:Mathematics; D008121:Nephropidae / Q000032:analysis*; D011485:Protein Binding
D008024:Ligands; D046911:Macromolecular Substances; D006433:Hemocyanins; D002118:Calcium