BIOSYNTHESIS OF THE PHYTOTOXIN TENTOXIN .2. CELL-FREE BIOSYNTHESIS OFTENTOXIN - FIRST EVIDENCE ON THE LOCALIZATION OF TOXIN SYNTHESIS IN ALTERNARIA-ALTERNATA

In contrast to mechanical disruption of Alternaria alternata mycelia, disintegration of protoplasts by osmotic shock made it possible for th e first time to develop a cell-free system that produces tentoxin with out significant loss of enzyme activity. After separation of groups of cell organelles by fractional centrifugation, the main activity of te ntoxin synthesis was detectable in the membrane/microsome fraction and in the plasma fraction. The proteins in the plasma seem not to be sol uble. They are probably combined with lipids or small bits of membrane debris. For this reason, these proteins cannot be removed by ultracen trifugation. On the other hand, it is possible to precipitate the enzy me system with 2% NaCl. Disruption of cellular substructures (membrane s?) by mechanical disintegration or by various detergents led to a rap id loss of enzyme activity. The tentoxin-synthesizing enzyme is probab ly localized at or in membranes. De novo synthesis of tentoxin in a ce ll-free system devoid of ribosomes from radioactively labeled amino ac ids shows that tentoxin is not a virus product.