PMID- 10423253
OWN - NLM
STAT- MEDLINE
DCOM- 19990819
LR  - 20071114
IS  - 0006-2960 (Print)
IS  - 0006-2960 (Linking)
VI  - 38
IP  - 30
DP  - 1999 Jul 27
TI  - The intraflavin hydrogen bond in human electron transfer flavoprotein modulates
      redox potentials and may participate in electron transfer.
PG  - 9735-45
AB  - Electron-transfer flavoprotein (ETF) serves as an intermediate electron carrier
      between primary flavoprotein dehydrogenases and terminal respiratory chains in
      mitochondria and prokaryotic cells. The three-dimensional structures of human and
      Paracoccus denitrificans ETFs determined by X-ray crystallography indicate that
      the 4'-hydroxyl of the ribityl side chain of FAD is hydrogen bonded to N(1) of
      the flavin ring. We have substituted 4'-deoxy-FAD for the native FAD and
      investigated the analog-containing ETF to determine the role of this rare
      intra-cofactor hydrogen bond. The binding constants for 4'-deoxy-FAD and FAD with
      the apoprotein are very similar, and the energy of binding differs by only 2
      kJ/mol. The overall two-electron oxidation-reduction potential of 4'-deoxy-FAD in
      solution is identical to that of FAD. However, the potential of the
      oxidized/semiquinone couple of the ETF containing 4'-deoxy-FAD is 0.116 V less
      than the oxidized/semiquinone couple of the native protein. These data suggest
      that the 4'-hydoxyl-N(1) hydrogen bond stabilizes the anionic semiquinone in
      which negative charge is delocalized over the N(1)-C(2)O region. Transfer of the 
      second electron to 4'-deoxy-FAD reconstituted ETF is extremely slow, and it was
      very difficult to achieve complete reduction of the flavin semiquinone to the
      hydroquinone. The turnover of medium chain acyl-CoA dehydrogenase with native ETF
      and ETF containing the 4'-deoxy analogue was essentially identical when the
      reduced ETF was recycled by reduction of 2,6-dichlorophenolindophenol. However,
      the steady-state turnover of the dehydrogenase with 4'-deoxy-FAD was only 23% of 
      the turnover with native ETF when ETF semiquinone formation was assayed directly 
      under anaerobic conditions. This is consistent with the decreased potential of
      the oxidized semiquinone couple of the analog-containing ETF. ETF containing
      4'-deoxy-FAD neither donates to nor accepts electrons from electron-transfer
      flavoprotein ubiquinone oxidoreductase (ETF-QO) at significant rates (</=0.5% the
      wild-type rates). These results indicate that the 4'-hydroxyl-N(1) hydrogen bond 
      plays a major role in the stabilization of the anionic semiquinone and anionic
      hydroquinone oxidation states of ETF and that this hydrogen bond may provide a
      pathway for electron transfer between the ETF flavin and the flavin of ETF-QO.
FAU - Dwyer, T M
AU  - Dwyer TM
AD  - Department of Pediatrics, Cell and Developmental Biology Program, University of
      Colorado School of Medicine, Denver 80262, USA.
FAU - Mortl, S
AU  - Mortl S
FAU - Kemter, K
AU  - Kemter K
FAU - Bacher, A
AU  - Bacher A
FAU - Fauq, A
AU  - Fauq A
FAU - Frerman, F E
AU  - Frerman FE
LA  - eng
GR  - DK49726/DK/NIDDK NIH HHS/United States
GR  - HD04024/HD/NICHD NIH HHS/United States
PT  - Journal Article
PT  - Research Support, U.S. Gov't, P.H.S.
PL  - United States
TA  - Biochemistry
JT  - Biochemistry
JID - 0370623
RN  - 0 (Electron-Transferring Flavoproteins)
RN  - 0 (Flavins)
RN  - 0 (Flavoproteins)
RN  - 146-14-5 (Flavin-Adenine Dinucleotide)
RN  - 57818-88-9 (1-deaza-FAD)
SB  - IM
MH  - Animals
MH  - Electron Transport
MH  - Electron-Transferring Flavoproteins
MH  - Flavin-Adenine Dinucleotide/analogs & derivatives/chemistry
MH  - Flavins/*chemistry/metabolism
MH  - Flavoproteins/*chemistry/metabolism
MH  - Humans
MH  - Hydrogen Bonding
MH  - Kinetics
MH  - Oxidation-Reduction
MH  - Paracoccus denitrificans/chemistry
MH  - Spectrophotometry, Ultraviolet
MH  - Swine
EDAT- 1999/07/28 00:00
MHDA- 1999/07/28 00:01
CRDT- 1999/07/28 00:00
PHST- 1999/07/28 00:00 [pubmed]
PHST- 1999/07/28 00:01 [medline]
PHST- 1999/07/28 00:00 [entrez]
AID - 10.1021/bi9903906 [doi]
AID - bi9903906 [pii]
PST - ppublish
SO  - Biochemistry. 1999 Jul 27;38(30):9735-45. doi: 10.1021/bi9903906.