title: Characterization of heart cytosolic proteins capable of modulating calcium uptake by the sarcoplasmic reticulum. 1. Isolation of a protein with protective activity and its identification as muscle albumin.
abstract: A new type of regulation of the Ca-pumping activity of isolated sarcoplasmic reticulum membranes has been investigated. An inhibitory and an antagonistic fraction were obtained after (NH4)2SO4 fractionation of cardiac muscle cytosol according to a published procedure [Narayanan et al. (1983) Biochem. Biophys. Acta 735, 53-66]. The former fraction inhibited Ca uptake by sarcoplasmic reticulum vesicles in a concentration-dependent way. The inhibition could be prevented and even reversed by addition of the antagonistic fraction. The protein components of this latter fraction were resolved and separated using an anion-exchange chromatographic procedure (mono Q column in an FPLC system). A pure protein component with antagonistic properties was isolated. Biochemical (molecular mass, tryptic digestion pattern and antagonistic activity) and immunological (cross-reactivity with specific antibodies) analysis resulted in the identification of the purified antagonist protein as muscle albumin, a serum-albumin-like protein which is localized near the A/I junctions in the striated muscle cells. The protein may be involved in the regulation of Ca fluxes across the cisternal compartments of the sarcoplasmic reticulum.
mesh_terms: D000818:Animals; D001011:Aorta / Q000378:metabolism; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004285:Dogs; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000378:metabolism; D009132:Muscles / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D011506:Proteins / Q000502:physiology*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D011506:Proteins; D000252:Calcium-Transporting ATPases; D002118:Calcium