Proton relaxation studies of the interaction of small molecules with cytochrome P450
Philson, Stephen Baker
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/25631
Description
Title
Proton relaxation studies of the interaction of small molecules with cytochrome P450
Author(s)
Philson, Stephen Baker
Issue Date
1977
Doctoral Committee Chair(s)
Debrunner, Peter G.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
proton relaxation
small molecule interactions
cytochrome P450
small molecule-proton complex
Language
en
Abstract
The effect of ferric cytochrome P450 on the proton relaxation
cam times of a variety of small molecules has been studied. In some cases, Fe-proton distances in the small molecule-protein complex are determined. For water protons the following results are obtained: The substrate (camphor) complex of P450, which is in a mainly high-spin ferric state, has little effect on H20 relaxation times, suggesting that the heme iron may be five-coordinate. On the other hand, the native, predominantly low-spin P450 has a large effect on the water. From the frequency and
temperature dependence of the latter effect all the parameters associated
with the relaxation are obtained. One or two exchangeable protons are clearly bound to an axial ligand of the iron. Among potential ligands, carboxylic acids, methionine, histidine, and cysteine can be definitely ruled out as causing the effect; this leaves hydroxyl, amine, and amide groups as possiblities, in addition to H0.
2Relaxation of the methyl protons of 2-methylpyridine by P450 indicates that the low-spin iron in the methylpyridine complex has an electron
spin relaxation time TS of ~ 2 x 10-12 sec. This may be compared to the Ts for the native P450 of 5 x 10-10 sec, as derived from the frequency dependence of the water proton relaxation times. These TS values suggest that the relaxation effect of native P450 may be due not to the low-spin iron, but to a small high-spin fraction.
Relaxation of the methyl protons of 5-exo-hydroxycamphor, the product of the reaction catalyzed by P450, is also studied. The effect of the protein is substantially smaller on the C-9 protons than on the others, suggesting orientation of the hydroxyl end of the molecule toward the heme
iron and with an Fe-O distance of as little as 3 A. If camphor binds in
the same way, it is ideally positioned for hydroxylation at the C-5 position by an Fe-02 complex.
Relaxation studies of camphor protons are reported; however, their interpretation is difficult because of the complexity of the binding reaction. This complexity is evident from optical absorption measurements, which are also discussed.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
