BIOCHEMICAL STUDIES OF CALRETININ

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This work was aimed towards determining the biochemical function of calretinin. The initial results describe some of the basic characteristics of calretinin and will serve as the basis of further studies. These include the following: (1) Calretinin was identified in membrane fractions of rat cerebellum by both radioimmunoassay and immunoblot. Calcium produced an increase in the amount of calretinin associated with the synaptic membrane fraction and decreased the calretinin in cytosol relative to that found in the presence of EGTA; (2) Several approaches were used to search for calretinin target proteins. Iodinated calretinin was found to bind to proteins in several subcellular fractions on nitrocellulose blots of one dimensional SDS gels; (3) A purification procedure was developed for obtaining large amounts of homogeneous recombinant calretinin from plasmids. No differences were found in the physicochemical properties of native and recombinant calretinin (molecular weight, isoelectric point, calcium binding kinetics and behavior on ion exchange: gel filtration and hydrophobic columns); (4) A series of experiments used specific resins to study the hydrophobic properties of calretinin and the resins. A partial calcium dependence of calretinin binding observed for some resins (octylsepharose) was dependent on ionic strength and pH.