Metabolism of tetraorganolead compounds by rat-liver microsomal mono-oxygenase. III. Enzymic dealkylation of tetramethyl lead compared with tetraethyl lead.

The enzymic transformation of tetramethyl lead (PbMe4) to the trimethyl lead cation is very rapid with sp. activities of 40-50 nmol/min per mg protein. The reaction has an apparent Km of 1.28 X 10(-5) M. PbMe4 binds to cytochrome P-450 with a type 1 difference spectrum, Ks is 6.65 X 10(-6) M. Comparison of the data with results previously obtained for lead tetraethyl (PbEt4) shows that the 20 times higher metabolic rates observed with PbMe4 are related to an intrinsic higher O2 activation as well as to a more effective O2 utilization by that substrate.