INHIBITION BY POLYPHOSPHATE OF PHYTOPATHOGENIC POLYGALACTURONASES FROM BOTRYTIS-CINEREA

Polygalacturonase activity from the phytopathogenic fungus Botrytis ci nerea was inhibited in vitro by extracellular polyphosphate from Strep tomyces sp. A50, as well as other polyphosphates of biological and che mical origin. The extent of inhibition increased with polyphosphate ch ain length between 20 and 100 P-i residues. Although the activity of p olygalacturonase from B. cinerea appeared not to depend on the presenc e of cations, inhibition was partially blocked by divalent cations suc h as Mg2+ or Ca2+. Production of polyphosphate in Streptomyces sp. A50 was followed by chemical measurements, as well as by in vivo P-31-NMR analysis. During the first 2 days of growth, polyphosphate accumulate d within the cells, after which it appeared in the broth as an extrace llular product. A maximum concentration of extracellular polyphosphate (1 mM P-i equivalent) was reached, corresponding to about 25% of the input P-i. NMR analysis suggested that the intracellular form of polyp hosphate exists as a mobile soluble pool. In contrast, the extracellul ar form of polyphosphate appears to be complexed with cations.