Insoluble invertase from grapes: an artifact of extraction

Abstract

Both soluble invertase (supernatant from 10,000 g centrifugation) and insoluble invertase (precipitated with cell-wall fraction) were obtained from sultana grape berries homogenized under a variety of conditions. Treatment of the insoluble fraction with borate buffer, pH 8·5, polyethylene glycol (Carbowax 4000) or non-ionic detergents solubilized most of the invertase. Homogenates of grape berries prepared in the presence of Carbowax 4000, non-ionic detergents or protein (bovine serum albumin) contained up to 100 per cent of the total invertase in the soluble form. It is suggested that insoluble invertase from grapes is an artifact of extraction caused by the formation of a tannin-protein complex and/or a protein-tannin-cell-wall complex. Invertase in grapes is probably located in the cytoplasm or vacuoles of cells. In contrast to grapes, insoluble invertase from aged aseptic carrot disks or from corn coleoptiles could not be solubilized.