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Updated: Feb 2, 2026

A General Method for Detecting Nitrosamide Formation in the In Vitro Metabolism of Nitrosamines by Cytochrome P450s
Published on: September 25, 2017
Isoelectric point of free and adsorbed cytochrome c determined by various methods
Svetlana H Hristova1, Alexandar M Zhivkov2
1'Rostislaw Kaishew' Institute of Physical Chemistry, Bulgarian Academy of Sciences (BAS), Acad. G. Bonchev Str., bl. 11, Sofia 1113, Bulgaria; National Specialized Hospital for Active Treatment of Hematological Diseases, Plovdivsko pole Str. 6, Sofia 1756, Bulgaria.
Abstract:
The purpose is to determine the isoelectric point (IEP) pIμ of cytochrome c (cytC, a globular haemoproteid) adsorbed on montmorillonite (MM, plate-like colloid particles) by microelectrophoresis and to compare the pIμ value with pIf9.44 measured by isoelectric focusing in gel with covalently linked ampholytes, and with pInz10.0-10.6 of free cytC globule calculated by three programs for pH-dependent net charge nz using the crystallographic structure of cytC. The pH-dependence of the electrophoretic mobility μ(pH) in the range pH 6-11 shows out that IEP of cytC-MM particles appears at pH 9.35. The near courses of μ(pH) and nz(pH) reveal that the pH-independent negative charge of the MM substrate is hydrodynamically shielded by the adsorbed protein globules. The nearness of IEP and pIf allows attributing IEP value of cytC-MM particles to the isoelectric point pIμ of cytC. A short survey for pI of cytC reported in the literature since 1941 shows out that pI is dispersed in the range pH 9.0-10.65 although cytC is used now as pIf marker with well known IEP; the reason for that and the imperfections of the employed methods are discussed.
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