Chick 28,000 Mr vitamin D-dependent calcium-binding protein in intestine, kidney and cerebellum. Purification using chromatofocusing.

A purification method has been developed for chick 28,000 Mr vitamin D-dependent calcium-binding protein, involving Blue Sepharose CL-6B column chromatography, heat treatment and chromatofocusing with a microparticulate anion exchanger (Mono P). It allowed the rapid and reproducible purification of milligram amounts of homogeneous calcium-binding protein with good yields from chick intestine, kidney and cerebellum. The calcium-binding proteins thus obtained have the same molecular weight of 28,000, heat stability, calcium binding capability and apparent isoelectric point of 4.0. These physico-chemical properties are in good agreement with those of proteins isolated by a previous procedure, which gave a low and variable yield of calcium-binding protein.