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THE ROLE OF CALCIUM IONS IN THE ACTIVITY OF AN ENDO‐PECTIC ACID LYASE ON OLIGOGALACTURONIDES 1
Author(s) -
ATALLAH MOKHTAR T.,
NAGEL CHARLES W.
Publication year - 1977
Publication title -
journal of food biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.507
H-Index - 47
eISSN - 1745-4514
pISSN - 0145-8884
DOI - 10.1111/j.1745-4514.1977.tb00180.x
Subject(s) - tetramer , chemistry , calcium , enzyme , substrate (aquarium) , biochemistry , dissociation constant , lyase , stereochemistry , organic chemistry , biology , ecology , receptor
A pectic acid lyase was purified from the culture filtrates of Cephalosporium sp. Tetragalacturonic acid was the shortest chain of oligogalacturonides attacked and calcium ions were required for activity. The enzyme was most active at pH 9.9. The kinetic data showed that while Vmax was relatively constant, the Km decreased with increasing chain length of the substrate. The Km was independent of chain length for the substrates containing seven or more galacturonic acid units. Both kinetic data and paper chromatographic analyses of degradation products from the different oligomers indicated that the enzyme was an endo‐pectic acid lyase. In the presence of 0.002 N Cacl 2 , substrate (tetramer through octamer) concentrations above 0.001 N caused inhibition of activity. The role of calcium was studied by measuring enzymic activity at different concentrations of calcium and tetramer. The data indicated that the true substrate for the lyase activity was the calcium salt of tetramer. The observed substrate inhibition was due to competition between the free oligomer and its calcium salt. The dissociation constant (K i ) for the tetramer as an inhibitor was 1.25 mM and the Km for the calcium salt was 0.14 mM. The data also suggested the possible additional role of calcium as an activator for the lyase.