POLY(BETA-L-MALATE) HYDROLASE FROM PLASMODIA OF PHYSARUM-POLYCEPHALUM

A 68-kDa extracellular glycoprotein from Physarum polycephalum that hy drolyses specifically poly(beta-L-malic acid) by removing monomers of L-malic acid in an exolytic manner has been purified and characterized . The enzyme was purified 1740-fold from the culture medium by ammoniu m sulfate precipitation, hydrophobic interaction chromatography on but yl-Toyopearl, and gel permeation chromatography on Superdex 200 to a s pecific activity of 9.0 mu mol . min(-1). mg(-1). The hydrolase was al so purified from the cytosol, which contained 1 mg in 43 g cells in co ntrast to 1 mg extracellular enzyme in 28 L of culture medium. The pH optimum was pH 3.5 as a result of the effect of an acidic side chain o n V-max and the preferred binding of poly(beta-L-malate) in the ionize d form. Intracellular hydrolase was only marginally active on [C-14]po ly(beta-L-malate) that had been injected into plasmodia. Poly(L-aspart ate), poly(L-glutamate), poly(vinyl sulfate), and poly(acrylate) were neither bound nor degraded by the hydrolase, Poly(beta-hydroxybutyric acid), which was considered the reduced form of poly(beta-L-malate), w as not a substrate. The enzyme is neither a metallo- nor a serine-este rase, and is distinct from poly(3-hydroxybutyric acid) depolymerases. It is related to a glucosidase with respect to hydrophobic interaction chromatography? the pH-activity dependence, and its inhibition with m ercuribenzoate. N-bromosuccinimide, and D-gluconolactone, but not the use of the substrates.