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Studies in the Physiology of Parasitism: XVIII. Pectic Enzymes secreted by Bacterium aroideae

R. K. S. WOOD
Annals of Botany
New Series, Vol. 19, No. 73 (January 1955), pp. 1-27
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/42907263
Page Count: 27
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Studies in the Physiology of Parasitism: XVIII. Pectic Enzymes secreted by Bacterium aroideae
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Abstract

Cell-free filtrates from cultures of Bacterium aroideae on a simple synthetic medium contained an enzyme, provisionally termed depolymerase, which rapidly reduced the viscosity of pectin solutions, and protopectinase which macerated slices of potato tuber tissue. These filtrates had little pectin-esterase activity. The activity of depolymerase was directly proportional to enzyme concentration ; the activity of protopectinase was approximately proportional to the square root of the enzyme concentration. Crude solutions were partially purified by acetone or ethanol precipitation; ammonium sulphate was less satisfactory as a precipitating agent. Enzyme preparations which rapidly reduced the viscosity of pectin and pectate solutions were relatively inactive when assayed for polygalacturonase activity by measuring reducing groups liberated. After prolonged incubation some 20 and 40 per cent, hydrolysis of solutions of pectin and pectate respectively was obtained. The pH optimum for depolymerase activity was near 9·0, the enzyme was activated by Ca⁻⁺ but not by a number of other cations; the loss of activity following dialysis was largely restored by adding Ca⁺⁺. The enzyme was rapidly inactivated at temperatures above 60° C. and at pH 2·7. The properties of protopectinase generally resembled those of depolymerase. Analysis of the breakdown products following enzyme degradation of pectin and pectate solutions by paper chromatography showed that galacturonic acid was not produced but that a number of other products were formed, including one of fairly low molecular weight. The differences between the pectic enzymes of B. aroideae and those from other sources, and the possible identity of depolymerase, polygalacturonase, and protopectinase are discussed.

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