TY - JOUR
T1 - Effect of disordered hemes on energy transfer rates between tryptophans and heme in myoglobin
AU - Gryczynski, Z.
AU - Fronticelli, C.
AU - Tenenholz, T.
AU - Bucci, E.
N1 - Funding Information:
This work was supported in part by National Institutes of Health grants HL-13164 and HL-36229. Computer time and facilities were supported in part by the Computer center facilities of the University of Maryland at College Park and Baltimore campuses.
Funding Information:
Received for publication 16 April 1993 and in final form 10 August 1993. Address reprint requests to Dr. Enrico Bucci at the Department of Biological Chemistry, University of Maryland at Baltimore, 108 N. Greene St., Bal- timore, MD 21201. *Recipient of the fellowship from the American Heart Association, Mary- land Affiliate. Abbreviations used: Mb, myoglobin; CO-Mb, carbon monoxy myoglobin; deoxy-Mb, unliganded myoglobin; Met-Mb, ferric myoglobin; TrP, tryp- tophan; PVA, polyvinyl alcohol; SW, sperm whale. X) 1993 by the Biophysical Society 0006-3495/93/11/1951/08 $2.00
PY - 1993
Y1 - 1993
N2 - Our recent linear dichroism study of heme transitions (Gryczynski, Z., E. Bucci, and J. Kusba. 1993. Photochem. Photobiology. in press) indicate that heme cannot be considered a planar oscillator when it acts as an acceptor of radiationless excitation energy transfer from tryptophan. The linear nature of the heme absorption transition moment in the near-UV region implies a strong dependence of the transfer rate factors on the relative angular position of the heme and tryptophan, i.e., on the kappa 2 orientation parameter of the Förster equation. Using the atomic coordinates of SW myoglobin we have estimated the variation of kappa 2 parameter as a function of the heme absorption transition moment direction. The simulations proved that transfer is very efficient and anticipates lifetimes in the picosecond range. Also, they showed that transfer is very sensitive to rotations of the heme around its alpha-gamma-meso-axis, which may reduce the efficiency of transfer to almost zero values, producing lifetimes very similar to those of free tryptophan, in the nanosecond range. Comparisons between the lifetime values reported in the literature and those here estimated suggest that natural heme disorder, in which heme is rotated 180 degrees around its meso axis, is at the origin of the nanosecond lifetimes found in myoglobin systems.
AB - Our recent linear dichroism study of heme transitions (Gryczynski, Z., E. Bucci, and J. Kusba. 1993. Photochem. Photobiology. in press) indicate that heme cannot be considered a planar oscillator when it acts as an acceptor of radiationless excitation energy transfer from tryptophan. The linear nature of the heme absorption transition moment in the near-UV region implies a strong dependence of the transfer rate factors on the relative angular position of the heme and tryptophan, i.e., on the kappa 2 orientation parameter of the Förster equation. Using the atomic coordinates of SW myoglobin we have estimated the variation of kappa 2 parameter as a function of the heme absorption transition moment direction. The simulations proved that transfer is very efficient and anticipates lifetimes in the picosecond range. Also, they showed that transfer is very sensitive to rotations of the heme around its alpha-gamma-meso-axis, which may reduce the efficiency of transfer to almost zero values, producing lifetimes very similar to those of free tryptophan, in the nanosecond range. Comparisons between the lifetime values reported in the literature and those here estimated suggest that natural heme disorder, in which heme is rotated 180 degrees around its meso axis, is at the origin of the nanosecond lifetimes found in myoglobin systems.
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U2 - 10.1016/S0006-3495(93)81266-9
DO - 10.1016/S0006-3495(93)81266-9
M3 - Article
C2 - 8298024
AN - SCOPUS:0027435140
SN - 0006-3495
VL - 65
SP - 1951
EP - 1958
JO - Biophysical journal
JF - Biophysical journal
IS - 5
ER -