Abstract

The soluble proteins obtained by osmotic lysis of time catecholamine storage vesicles have been purified by chromatography on DEAE-cellulose and Sephadex G-200. The major protein fraction (S₁) appears to be highly purified: it sedimented as a single homogeneous fraction in the ultracentrifuge; it gave, with few exceptions, a single protein spot upon electrophoresis at different pH values, and its amino acid composition and fingerprints of tryptic digests were constant from preparation to preparation. Immunological and enzymic analysis of this protein indicated that it contained less than 1% of highly immunogenic contaminants, one of which was dopamine-β-oxidase.

In addition to the major protein fraction, two other protein peaks were obtained from the Sephadex G-200 column. One of these (S₂) appeared homogeneous in the ultracentrifuge and had an S_25,w of 1.4 at a protein concentration of 3 mg/ml. This fraction was less pure than S₁.

Studies of the amino acid composition, fingerprints of tryptic digests and the molecular weight of S₁ indicate that the protein may consist of two identical subunits having a molecular weight of 40,000. Time data are consistent with a unit structure of (a) a single peptide chain with one intrachain disulfide bond, or (b) two or more different chains with one intra- or one interchain disulfide bond.

Studies of time binding capacity of S₁ showed that it did not, by itself, or in the presence of Mg⁺⁺ and ATP, bind sufficient amounts of catecholamines to be able to account for the stability of a significant fraction of the catecholamines within the storage vesicles.