Three Ca2+-binding proteins from porcine liver and intestine differ immunologically and physicochemically and are distinct in Ca2+ affinities.

摘要: Intestinal brush-border-derived membrane vesicles contain, after demembranation in the presence of Ca2+, a subset polypeptides that are specifically solubilized by addition Ca2+ chelators. As described previously, this fractionation scheme leads to enrichment two major proteins (I and II), one which has been shown be identical cellular p36K target Rous sarcoma virus-encoded tyrosine-specific protein kinase (Gerke, V., Weber, K., (1984) EMBO J. 3, 227-233). We have applied similar protocol from porcine liver purified third Ca2+-binding (III). All three had wide tissue distributions, were absent brain, red blood cells, cardiac skeletal muscle. Relative amounts varied between tissues, with I low III very intestine. Despite their extractability (I, II, III) clearly distinct as far immunological, biochemical, physicochemical properties concerned. They also show characteristic differences affinities for ions. The association constants binding estimated means indirect methods 10(4) M-1 (protein I) 10(6) III), while direct Hummel-Dreyer method reveals characterized an constant 0.4 X 10(5) absence 0.2 2 mM MgCl2. Conformational changes upon II using circular dichroism, fluorescence emission, UV difference spectra. These alterations could attributed increased exposure tyrosine tryptophan residues more aqueous environment, led hydrophobicity would explain observed Ca2+-dependent interaction hydrophobic matrices like phenyl-Sepharose.