The affinity of human erythrocyte porphobilinogen synthase for Zn2+ and Pb2+.
Porphobilinogen synthase activity has been measured in human erythrocyte lysates supplemented with metal-ion buffers to control free Zn2+ and Pb2+ concentrations. The enzyme is activated by Zn2+ with a Km of 1.6 pM and inhibited by Pb2+ with a Ki of 0.07 pM. Pb2+ and Zn2+ appear to compete for a single metal-binding site. The half-time for loss of Zn2+ from the active site, or replacement of Pb2+ by Zn2+, were in the 10-20-min range at 37 degrees C. Zn2+ did not affect the affinity for the substrate 5-aminolevulinate, but Pb2+ reduced it non-competitively. All the experiments were conducted with a blood sample of the common 1-1 phenotype [Astrin, K. H., Bishop, D. F., Wetmur, J. G., Kaul, B., Davidow, B. & Desnick, R. J. (1987) Ann. NY Acad. Sci. 514, 23-29].
Simons
T J
TJ
Biomedical Sciences Division, King's College London, UK.
D004912:Erythrocytes / Q000201:enzymology*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D007854:Lead / Q000378:metabolism*; D000623:Porphobilinogen Synthase / Q000378:metabolism*; D013379:Substrate Specificity; D015032:Zinc / Q000378:metabolism*
D007854:Lead; D000623:Porphobilinogen Synthase; D015032:Zinc