RESTORATION OF LEAD-INHIBITED 5-AMINOLEVULINATE DEHYDRATASE ACTIVITY IN WHOLE-BLOOD BY HEAT, ZINC ION, AND (OR) DITHIOTHREITOL

Abstract

Effects of heat, Zn ion and dithiothreitol in restoring the activity of Pb-inhibited 5-aminolevulinate dehydratase (EC 4.2.1.24) were examined. The ratio of non-activated to activated activity produced by dithiothreitol correlated well with blood Pb concentration among 35 lead workers. The individual effects of heat, Zn or dithiothreitol differ from each other in the shift of pH optimum, and in the extent to which activity is restored. Dual or triple combinations of these agents show additive or complementary restoration of activity. The combination of heat and Zn, or Zn and dithiothreitol expands the range of optimum concentration of Zn in restoring activity. Using these combinations of agents, more accurate evaluation of Pb exposure can be expected than by measuring only activation by Zn. Although dithiothreitol most powerfully restores activity, it restores not only the activity inhibited by Pb exposure, but also the activity removed by oxidation of SH-groups in the enzyme molecule.