Polygalacturonic acid trans-eliminase of Xanthomonas campestris

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Abstract
Polygalacturonic acid trans-eliminase from the culture fluid of X. campestris was purified 66-fold by acetone precipitation, citrate extraction and chromatography on diethylaminoethyl- and carboxymethyl-cellulose. The optimum pH is 9.5 in glycine-sodium hydroxide buffer. Up to lm[image]-calcium chloride brings about a remarkable stimulation of the enzyme activity and, at this concentration, no other cations promote or inhibit enzyme action except Ba2+ ions, which cause complete inhibition. The enzyme degrades polygalacturonic acid in a random manner; it does not act upon polygalacturonate methyl glycoside, although it can cleave partially (68%) esterified pectin. The end products from polygalacturonic acid at 46% breakdown are unsaturated di- and tri-galacturonic acids, in addition to saturated mono-, di- and tri-galacturonic acids. Pentagalacturonic acid is split preferentially into saturated dimer plus unsaturated trimer, or into saturated trimer plus unsaturated dimer; at a lower rate, it is also split into monomer and unsaturated tetramer. Unsaturated pentamer is split into unsaturated dimer plus unsaturated trimer. Tetragalacturonic acid is split some-what preferentially at the central bond to form dimer and unsaturated dimer, but it is also split into monomer and unsaturated trimer. Un-saturated tetramer is split only at the central bond to yield only un-saturated dimer. Trigalacturonic acid is split into monomer and unsa-turated dimer. Unsaturated trimer is cleaved into saturated dimer and probably-4-deoxy-L-5-threo-hexoseulose uronic acid, which has not yet been directly identified. Neither saturated nor unsaturated digalacturonic acid is attacked. The unsaturated digalacturonic acid was isolated and proved to be O-(4-deoxy-[beta]-L-5-threo-hexopyranos-4-enyluronic acid)-(1[forward arrow]4)-D-galacturonic acid.