Abstract
A protein fraction having a high binding affinity to catecholamine was isolated from mouse brain. This purified brain protein was prepared by extraction with pH 7.3 Tris-phosphate buffer, ultracentrifugation, 30–50% saturated ammonium sulfate precipitation and DEAE-cellulose chromatography. The effect of various physicochemical treatments on the specific binding activity of the brain protein to [ 3Hnorepinephrine was determined. Enzymatic digestion with trypsin, pronase or neuraminidase, heating at 56°C and treatment with EDTA or nucleotides significantly diminished the binding activity. The purified brain protein had a molecular weight of 78,000. A Scatchard plot indicated that it contained two binding sites with apparent dissociation constants of2.34 × 10 −8 Mand4.74 × 10 −7 M. The polyacrylamide gel electrophoretic pattern of the brain protein revealed two distinct fractions A and B. Protein fraction A had a stronger affinity for binding norepinephrine; it was markedly inhibited by neuraminidase and trypsin but not by phenoxybenzamine and propranolol, while protein fraction B was markedly inhibited by propranolol but not by neuraminidase.
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