title: Replacement of metal in metalloenzymes. A lead-alkaline phosphatase.
abstract: Lead ions can interact with calf intestine alkaline phosphatase. Experiments using 203Pb-labeled Pb2+ ions showed that Pb2+ ions bind the native protein in a molar ratio of Pb/protein of 1:5 with moderate inhibition of its biochemical activity. The 4 g-atoms of Zn per mol present in the native enzyme may be removed by dialysis against EDTA. The inactive apoenzyme is capable of incorporating Pb2+ ions in a Pb/protein molar ratio of 2:1, giving a lead-protein complex still enzymatically active also when genetic material, such as nucleotides or DNA, has been used a a substrate. The reconstituted lead-protein is capable of binding Zn2+ ions without any release of the Pb2+ ions and with an increase in the catalytic activity of only 10-15%. The absence of Zn in the inactive apoenzyme as well as in the reconstituted lead-protein, the incorporation of Pb2+ ions in stoichiometric amounts in the apoenzyme, and the weak influence of the Zn2+ ions on the enzymatic assay of the lead-enzyme suggest that lead ions partially reactivate the calf intestine alkaline phosphatase apoenzyme.
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001051:Apoenzymes; D001665:Binding Sites; D002417:Cattle; D004492:Edetic Acid; D004926:Escherichia coli / Q000201:enzymology; D007421:Intestine, Small / Q000201:enzymology; D007700:Kinetics; D007854:Lead / Q000494:pharmacology; D011485:Protein Binding; D013045:Species Specificity; D015032:Zinc
chemical_list: D001051:Apoenzymes; D007854:Lead; D004492:Edetic Acid; D000469:Alkaline Phosphatase; D015032:Zinc