Molecular Pharmacology, Vol 16, 242-249, Copyright © 1979 by the American Society for Pharmacology and Experimental Therapeutics

Electrophoretic Characterization of Monoamine Oxidase by [³H]Pargyline Binding in Rat Hepatoma Cells with A and B Activity

¹ Department of Human Genetics, Yale University School of Medicine New Haven, Connecticut 06510

[³H]Pargyline bound to active sites of both A and B types of monoamine oxidase (MAO) activity in a clonal line of rat hepatoma cells. Crude mitochondrial preparations were incubated with this drug, washed and solubilized, then electrophoresis was carried out in sodium dodecyl sulfate (SDS) polyacrylamide gels. At [³H]pargyline concentrations up to 2 nmoles/mg mitochondrial protein (0.8 µM), a single major protein species of molecular weight 57,000 was identified by autoradiography. The dose-dependent inhibition of labeling of this protein band by clorgyline and deprenyl was consistent with the presence of both A and B sites of MAO. Moreover, both A and B types of activity were inhibited under conditions giving saturated binding of [³H]pargyline to the 57,000 dalton protein Our results support the hypothesis that MAO activity resides in one protein or several proteins of similar molecular weight.

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ACKNOWLEDGMENTS We thank Dr. John Casnellie for his excellent advice throughout this study; Drs. Dennis Murphy and Jonathan Costa for suggesting the use of radioactively labeled pargyline; and Ms. Lisa Poteet and Regina Gambardella for skilled preparation of the manuscript.