ERYTHROCYTIC DELTA-AMINOLAEVULINATE DEHYDRATASE: A POTENTIAL BIOLOGIC INDEX OF EXPOSURE TO TOXIC METALS.

摘要

The reliability, sensitivity, specificity and applicability of a test based upon the measurement of the activity of the erythrocytic enzyme (delta)-aminolaevulinic acid dehydratase, in its present or altered form, as a viable alternative to other presently accepted biological indices of intoxications by lead, zinc, cadmium, copper and mercury present in the workplace and/or urban environment were thoroughly investigated.;A study of the metals of interest, both "in vivo" and "in vitro", revealed that they can radically influence enzyme measurement at pH values in the range 5.8 to 7.4 and, thus, seriously prejudice the results of an assay performed at a single pH value. A search for an alternative, improved assay led to the development of a test based upon the ratio of enzyme activity measured at specific pH values before and/or after pre-incubation of the buffered haemolysate. Tests conducted with several lead-exposed populations clearly demonstrated that the activity-ratios could function as biological indicators of lead intoxication and replace the presently accepted index namely, blood lead concentrations. The activity-ratios can also be used to monitor zinc or copper exposure although not with the same degree of sensitivity and specificity.;The study of the interaction of the metals of interest with the erythrocytic enzyme also shed new light upon its mechanism of action and several interpretations of these results are offered.;The investigation of procedural factors culminated in the development of a novel micro-assay procedure which requires only 10 (mu)L of human blood and effectively avoids procedural pitfalls.