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Electron Transfer Reactions of Candidate Tumor Suppressor 101F6 Protein, a Cytochrome b561 Homologue, with Ascorbate and Monodehydroascorbate Radical
journal contribution
posted on 2013-05-28, 00:00 authored by Mariam
C. Recuenco, Md. Motiur Rahman, Fusako Takeuchi, Kazuo Kobayashi, Motonari TsubakiThe candidate tumor suppressor 101F6
protein is a homologue of
adrenal chromaffin granule cytochrome b561, which is involved in the electron transfer from cytosolic ascorbate
to intravesicular monodehydroascorbate radical. Since the tumor suppressor
activity of 101F6 was enhanced in the presence of ascorbate, it was
suggested that 101F6 might utilize a similar transmembrane electron
transfer reaction. Detailed kinetic analyses were conducted on the
detergent-solubilized recombinant human 101F6 for its electron transfer
reactions with ascorbate and monodehydroascorbate radical by stopped-flow
and pulse radiolysis techniques. The reduction of oxidized 101F6 with
ascorbate was found to be independent of pH in contrast to those observed
for chromaffin granule and Zea mays cytochromes b561 in which both cytochromes exhibited very
slow rates at pH 5.0 but faster at pH 6.0 and 7.0. The absence of
the inhibition for the electron acceptance from ascorbate upon the
treatment with diethyl pyrocarbonate suggested that 101F6 might not
utilize a “concerted proton/electron transfer mechanism”.
The second-order rate constant for the electron donation from the
ascorbate-reduced 101F6 to the pulse-generated monodehydroascorbate
radical was found to be 5.0 × 107 M–1 s–1, about 2-fold faster than that of bovine chromaffin
granule cytochrome b561 and about five
times faster than that of Zea mays cytochrome b561, suggesting that human 101F6 is very effective
for regenerating ascorbate from monodehydroascorbate radical in cells.
Present observations suggest that 101F6 employs distinct electron
transfer mechanisms on both sides of the membranes from those of other
members of cytochrome b561 protein family.
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Keywords
pH 5.0electron transfer reactionscytosolic ascorbate101 F 6electron acceptancechromaffin granuleelectron donationelectron transfer mechanismsZea mays cytochromes b 561Candidate Tumor Suppressor 101 F 6 Proteindiethyl pyrocarbonateCytochrome b 561 Homologueelectron transferMonodehydroascorbate RadicalThe candidate tumor suppressor 101 F 6 proteinelectron Transfer Reactionscytochrome b 561 protein familytumor suppressor activitypulse radiolysis techniquesintravesicular monodehydroascorbatechromaffin granule cytochrome b 561pH 6.0Present observationstransmembrane electron transfer reaction
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