Deoxyriboaldolase (2-deoxy-d-ribose-5-phosphate acetaldehyde lyase, EC 22.214.171.124) from human erythrocytes was purified approx. 2500 times by treatment of hemolysates with (NH4)2SO4(25%) and two successive treatments with calcium phosphate gel. The enzyme was unstable in hemolysates (half life, 2 days) and partially purified preparations, but could be stabilized by 0.01 M MgCl2(half life, 4 days) or sulfhydrylreagents (dithiothreitol). The latter could also reactivate storage inactivated preparations. Erythrocyte deoxyriboaldolase was activated by dicarboxylic and tricarboxylic acids of which citrate was most effective and activated 2-3 fold. Cis-configuration activators (maleate) were more effective than trans-isomers (fumarate), indicating a proximity requirement for adjacent carboxyl groups of the activator. At several citrate concentrations uncompetitive activation kinetics were observed. Kmand vmaxfor the enzyme without citrate was 96 μM and 0.96 mM/h, and with 4 mM citrate was 361 μM and 4.17 mM/h, respectively. Additionally, citrate caused aggregation of the enzyme. © 1970.
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