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Updated: Jul 31, 2026

The Importance of Correct Protein Concentration for Kinetics and Affinity Determination in Structure-function Analysis
Published on: March 18, 2010
Three kinetically different inorganic phosphate entities in bovine casein micelles revealed by isotopic exchange
Zvonimir I Kolar1, Tona G Verburg, Hein J M van Dijk
1Department of Radiochemistry, Interfaculty Reactor Institute, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands. kolar@iri.tudelft.nl
Abstract:
Much controversy exists concerning the way calcium phosphate is linked to milk phosphoproteins including caseins. Homoionic exchange of inorganic phosphate between micellar calcium phosphates (MCP) of casein micelles and solute phosphates in cows' milk was investigated using H(32)PO(4)(2-) as radiotracer. Compartmental analysis and modelling revealed the presence of three MCP-related inorganic phosphate compartments each representing a separate phosphate entity. The relative phosphate quantities per compartment, i.e. the quantities of kinetically identical phosphate ions per MCP-ion cluster, and their mean residence times are 2:1:1 and 818, 0.24 and 23 h, respectively. Hence each MCP-ion cluster comprises four inorganic phosphate ions divided over three intra-MCP binding sites each characterised by a mean residence time for homomolecular phosphate exchange at solution/MCP interface.
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