Collect. Czech. Chem. Commun. 1998, 63, 1678-1682

Accessibility of Tyrosine Residues in Cytochrome P-450scc (CYP11A1)

Pavel Anzenbachera, Jiří Hudečekb, Reinhard Langec and Frédéric Bancelc

a Institute of Experimental Biopharmaceutics, Joint Institute of PRO.MED.CS Prague and of the Academy of Sciences of the Czech Republic, 500 02 Hradec Králové, Czech Republic
b Department of Biochemistry, Faculty of Science, Charles University, 128 40 Prague 2, Czech Republic
c INSERM Unite 128, Route de Mende 1919, 34233 Montpellier Cedex 5, France


Cytochrome P-450scc (CYP11A1) is known to exist in various conformational states. To study the accessibility of tyrosine residues to the solvent, second and fourth derivatives of cytochrome absorption spectra in the ultraviolet region were used. The measurements were carried out in the temperature range -10 to 40 °C and at two pH values (6.8 and 7.4). Our results indicate that the tyrosine residues of this enzyme are less accessible at higher temperatures as well as at higher pH, that is at conditions where the conformational equilibrium shifts to low-spin Fe(III) form(s). In other words, a more compact structure is attributable to the low-spin Fe(III) form(s) of P-450scc.

Keywords: Enzymes; Cytochromes P-450; CYP11A1; Derivative spectra; Steroid hormones biosynthesis.