A Caltech Library Service

Investigation of electron transfer in the [alpha]-helical protein cytochrome b [subscript 562]


Farrow, Neil (1999) Investigation of electron transfer in the [alpha]-helical protein cytochrome b [subscript 562]. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/8mrb-7d44.


Electron transfer rates in the [alpha]-helical protein cytochrome b[562] are investigated using the photoexciteable luminescent labelling compound ruthenium(II)bis(2,2'-bipyridine)(imidazole) attached to surface accessible histidine residues. Three residues on helices A and D and two on helix C were replaced with histidine by site directed mutagenesis to form eight mutant proteins which, together with a wild-type histidine on helix C, were labelled with ruthenium(II)bis(2,2'-bipyridine)(imidazole). Laser excitation of ruthenium(II)bis(2,2'-bipyridine)(imidazole) formed the highly reducing species *ruthenium(II)bis(2,2'-bipyridine)(imidazole) which was either quenched by the heme directly and the back rate (k[b][ET]) to the RuIII monitored by transient absorbance, or was oxidized by an external quencher and the rate from the reduced protein then monitored. Mutants spanned a metal-metal distance range from 14.2 Å to 25 Å with the rates ranging from 2.5 x 10[2] s[-1] to 2.2 x 107 s[-1]. A ß value of 1.09 Å[-1] is calculated from the data which agrees well with data from azurin and cytochrome c. The results show that the [alpha]-helices together with the extended heme plane provides an efficient homogenous barrier to electron transfer. A mutant of cytochrome b[562] with a covalently attached heme via one thioether linkage was expressed. The unfolding characteristics of this protein show it to be more stable to guanidinium unfolding than wild-type protein. The electron transfer rate for this mutant was identical to wild-type indicating minimal perturbation of the heme binding pocket by the mutation. It can be inferred that the side chain of the carboxyl terminal arginine residue and not Arg98 is responsible for stabilizing the His102 ligand histidinate charge.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Richards, John H.
Thesis Committee:
  • Richards, John H. (chair)
  • Parker, Carl Stevens
  • Gray, Harry B.
  • Winkler, Jay Richmond
  • Dervan, Peter B.
Defense Date:1 January 1999
Record Number:CaltechETD:etd-02082007-151616
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:557
Deposited By: Imported from ETD-db
Deposited On:06 Mar 2007
Last Modified:19 Apr 2021 22:39

Thesis Files

PDF (Farrow_n_1999.pdf) - Final Version
See Usage Policy.


Repository Staff Only: item control page