A SPECIFIC SOLUBLE PROTEIN FROM CATECHOLAMINE STORAGE VESICLES OF BOVINE ADRENAL MEDULLA .2. PHYSICAL CHARACTERIZATION

50% of the soluble protein of the chromaffin granules consists of a homogeneous protein. The protein has a molecular weight of 81 200 in neutral salt solutions as measured by rapid equilibrium osmometry. Molecular weight measurement by sedimentation equilibrium in 6 M guanidine·HCl with a reducing agent present shows that the protein is composed of two identical or nearly identical subunits of weight average mol. wt. 40 600. The protein is partially randomized at neutral pH at both ionic strengths 0.03 and 0.3, as indicated by a marked dependence of the sedimentation coefficient on protein concentration. However, at ionic strength 0.3, as the pH approaches the isoelectric pH (4.5), the protein is more compact and behaves in an almost globular manner. © 1969.