Changes in Haem Synthesis Associated with Occupational Exposure to Organic and Inorganic Sulphides

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Abstract
Analysis of reticulocytes for .delta.-amino-levulinic acid synthase (AmLev synthase, EC 2.3.1.37) and heme synthase (EC 4.99.1.1) activity in 17 workers in pulp production with low-level H2S and methylmercaptan exposure showed decreased activities in 8 and 6 cases, respectively. Erythrocyte protoporphyrin concentration was below the control range in 7 cases. Low AmLev synthase and heme synthase activities were found in 1 patient with H2S intoxication 1 wk after the event. The activities had returned to the control levels 2 mo. later, though erythrocyte protoporphyrin remained abnormally low. In vitro, H2S inhibited heme synthase with an apparent Ki [inhibition constant] of 3.4 mmol/l. Sulfide anion, on the other hand, inhibited AmLev synthase activity 85% at 10 mmol/l concentration. Thiosulfate anion inhibited AmLev synthase activity 18% and heme synthase activity 43% at 10 mmol/l concentration. Selenite inhibited AmLev synthase and heme synthase. The assay of AmLev synthase and heme synthase could be a valuable addition to the assessment of workers'' heath in industries generating H2S and/or methylmercaptan, although the mechanism of the toxic effect remains speculative.