Three kinetically different inorganic phosphate entities in bovine casein micelles revealed by isotopic exchange method and compartmental analysis.
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.
Kolar
Zvonimir I
ZI
Department of Radiochemistry, Interfaculty Reactor Institute, Delft University of Technology, Mekelweg 15, 2629 JB Delft, The Netherlands. kolar@iri.tudelft.nl
Verburg
Tona G
TG
van Dijk
Hein J M
HJ
D000818:Animals; D001665:Binding Sites; D002130:Calcium Phosphates / Q000737:chemistry; D002364:Caseins / Q000737:chemistry*; D002417:Cattle; D066298:In Vitro Techniques; D007700:Kinetics; D008823:Micelles; D008892:Milk / Q000737:chemistry; D008956:Models, Chemical; D010710:Phosphates / Q000737:chemistry*; D010761:Phosphorus Radioisotopes
D002130:Calcium Phosphates; D002364:Caseins; D008823:Micelles; D010710:Phosphates; D010761:Phosphorus Radioisotopes