[63] Dimethylpyrazole carboxamidine and related derivatives

Publisher Summary The frequency and great biological importance of divalent metal binding sites on proteins makes them of particular interest as the object of affinity labeling studies. Organic cations of many types interact with metal ion sites in biological materials; the binding of amidine and guanidinium compounds at these sites has been extensively studied. The chapter examines the principles involved in this affinity labeling technique to mitochondria by using a more hydrophobie derivative, 4-phenyl-3,5-dimethylpyrazole-1-carboxyamidine. It details the preparation reagents, preparation of affinity-labeled Pyruvate Kinase, and characterization of 4-Phenyl-3,5-Dimethylpyrazole-1-carboxamidine (PDMPA) as a Potential Affinity Label for Mitochondria. The chapter concludes that several unlabeled guanidinium compounds, including butylbiguanide, phenethylbiguanide, and phenethylguanidine, have been tested as potential binding competitors, hence protective ligands, but none are effective, nor is Ca2+ competitive. Conversely, unlabeled PDMPA does not compete for the nonenergized binding of 45Ca2+. 22.