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Title: A study of phosphoprotein and phosphopeptide interactions with calcium ions and dicalcium phosphate dihydrate crystals
Author: Muskett, Frederick W.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1993
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Phosphoproteins interact with calcium minerals in numerous biological systems but despite the importance of this phenomenon it is little understood. The interaction of phosphoproteins with calcium minerals is observed in milk where caseins interact with calcium phosphate to form micelles. Further understanding of this interaction was sought through two approaches. First, the adsorption isotherms for binding of the casein β-CN A and its N-terminal phosphopeptide (β-CN (f1-25)) to crystalline dicalcium phosphate dihydrate (DCPD) were measured. Secondly, attempts were made to grow co-crystals of calcium ions with phosphopeptides or with phosphoserine. A method of measuring phosphoprotein and phosphopeptide adsorption to DCPD was developed. From the adsorption isotherms the affinity and capacity of adsorption could be determined using a model of the adsorption process. Adsorption isotherms for β-CN A were all described using a simple Langmuir model of adsorption, adsorption occurring to identical and independent sites on the DCPD crystals. β-CN (f1-25) appears to adsorb to the same adsorption sites as β-CN A and also to a second family of adsorption sites which have a lower intrinsic affinity but which are more abundant. Adsorption isotherms for β-CN (f1-25) were described using a modified version of the Langmuir model in which there are two sets of adsorption sites. A term was included to allow for cooperative adsorption to the second set of adsorption sites. The effects of methylation of lysyl residues, buffer pH, incubation temperature, the presence of 6.0 M urea in the buffer and of crystal size were all examined. The adsorption of β-CN (f1-25) to DCPD crystals appears to be athermal since the measured isotherm does not change significantly with temperature (over the measured range), requiring that adsorption is due to an entropy gain. Comparison of the results of the β-CN A and β-CN (f1-25) adsorption experiments suggests that adsorption probably occurs via the N-terminal region of β-CN A, consistent with the hypothesis that the binding of phosphoproteins to calcium minerals occurs primarily through their phosphoseryl residues.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available