Fred K. Friedman, Ph.D.

Fred K. Friedman received his Ph.D. degree in chemistry from Columbia University in New York in 1979, where he studied immunoglobulin assembly and antibody-hapten interactions. He joined the Laboratory of Chemical Biology, NIADDK for a three year postdoctoral fellowship in the area of hemoglobin chemistry. In 1982 he joined the Laboratory of Molecular Carcinogenesis, where his research centers on structure, function and regulation of cytochrome P450.

RESEARCH

Structure-function of Cytochrome P450: The multiple forms of cytochrome P450 metabolize a wide variety of xenobiotic compounds such as drugs and carcinogens, as well as endobiotics such as prostaglandins and steroids. We apply biochemical, biophysical and computational approaches to examine the interactions of P450s with substrates, inhibitors, membrane lipids and microsomal proteins. Since these interactions modulate P450 activity, elucidation of their molecular mechanism will aid in a) clarifying the mechanism of P450 mediated drug and carcinogen metabolism, b) defining the role of individual P450s in the metabolism of endogenous and environmental chemicals and c) development of specific P450 inhibitors.

We employ the CO flash photolysis technique to study the binding kinetics of CO ligand to P450. This unique and powerful probe of P450 conformation/dynamics can be used to define fundamental P450-ligand and P450-substrate interactions in a native membrane environment. A kinetic difference method was developed to define the effect of substrates on specific P450s in microsomes which contain a multiplicity of P450 forms. Our results indicate that substrates can sterically hinder ligand binding and/or accelerate binding via conformational effects. Experiments with baculovirus expressed human P450s 1A1 and 3A4 show that these are not kinetically homogeneous but are composed of species with different conformations.

P450 interacts with NADPH cytochrome P450 reductase and cytochrome b5 during the catalytic cycle. We employed molecular graphics of P450 structures to predict P450 recognition sites for these electron carriers. Synthetic peptides corresponding to these regions on P450 2B1 were prepared and assessed for their ability to inhibit the P450 interaction with these proteins. The most potent peptide inhibitors were derived from combinations of P450 sequences that are proximate in the tertiary structure but distant in primary sequence. These results identify a reductase binding domain on the P450 surface and thus confirm a predicted feature of our P450 model.

 

 

1. Koley, A.P., Robinson, R.C., Markowitz, A. and Friedman, F.K.: Interaction of polycyclic aromatic hydrocarbons and flavones with cytochromes P450 in the endoplasmic reticulum: effect on CO binding kinetics. Biochemistry 34:1942-1947, 1995.
2. Koley, A.P., Robinson, R.C. and Friedman, F.K: Cytochrome P450 conformation and substrate interactions as probed by CO binding kinetics. Biochimie 78: 706- 713, 1996.
3. Adler, V., Pincus, M.R., Polotskaya, A., Montano, X., Friedman, F.K. and Ronai, Z.: Activation of C-jun-NH2-kinase by UV-irradiation is dependent on p21ras. J Biol Chem 38:23304-23309, 1996.
4. Koley, A.P., Dai, R., Robinson, R.C., Markowitz, A. and Friedman, F.K: Interaction of erythromycin with cytochromes P450 3A1/2 in the endoplasmic reticulum: a CO flash photolysis study. Biochemistry 36: 3237-3241, 1997.
5. Koley, A.P., Buters, J.T.M., Robinson, R.C., Markowitz, A. and Friedman, F.K.: Differential mechanisms of cytochrome P450 inhibition and activation by alpha-naphthoflavone. J Biol Chem 272: 3149-3153, 1997.
6. Sanna, M.T., Razynska, A., Karavitis, M., Koley, A.P., Friedman, F.K., Russu, I.M., Brinigar, W.S. and Fronticelli, C.: Assembly of human hemoglobin: studies with Escherichia coliexpressed alpha-globin.  J Biol Chem 272: 3478-3486, 1997.
7. Dai, R., Pincus, M.R. and Friedman, F.K.: Molecular modeling of cytochrome P450 2B1: mode of membrane insertion and substrate binding. J Prot Chem 17: 121-129, 1998.

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