β‐Granins: 21 kDa co‐secreted peptides of the insulin granule closely related to adrenal medullary chromogranin A

Abstract

Three closely related forms of a 21 kDa protein which is co‐secreted with insulin have been purified and analysed. These differed in behaviour on ion‐exchange chromatography but were indistinguishable by their susceptibility to staphylococcal V8 proteinase digestion, amino acid composition or N‐terminal amino acid sequence. Their amino acid composition and N‐terminal sequences were remarkably similar to adrenal medullary chromogranin A, a much larger protein (72 kDa). Antibodies to chromogranin A also reacted strongly with the 21 kDa protein in isolated insulin granules. It is concluded that the 21 kDa proteins either represent a repeated domain within the chromogranin molecule or a closely related gene product. The name β‐granin is proposed for these proteins.