Inactivation of solubilised fusicoccin-binding sites by endogenous plant hydrolases

The poor stability of crude solutions of fusicoccin-binding sites, prepared from acetonedried microsomal fractions of spinach leaves, results from the attack by endogenous phosphatase and -mannosidase. The addition of either of these enzymes to solubilised binding sites preincubated with ³H]fusicoccin promptly releases most of the bound radioactivity. A satisfactory stabilization of the crude preparations is obtained with fluoride added either during homogenization of the tissue, or immediately after solubilisation. The results indicate that the fusicoccin-binding sites are phosphorylated glycoproteins.Abbreviations FC fusicoccin - Tris/Mes 2-amino-2-(hydroxymethyl)-1,3-propanediol/2-(N-morpholino)ethanesulfonic acid This paper is dedicated to the memory of Eraldo Antonini, deceased 19 March 1983