82182065.Pdf
Total Page:16
File Type:pdf, Size:1020Kb
A42 HEMOGLOBINHIEMOGLOBIN AND MYOGLODINISYOGLOBIN M-Poe107 MPos108 LOW TEMPERATURE RECOMBINATION OF MbO, USING FOURIER TIME-RESOLVED X-RAY ABSORPTION SPECTROSCOPY ON A 5 ps TRANSFORM INFRARED SPECTROSCOPY. ((M. Halterman, L. M. Miller, and TIMESCALE. ((M.R. Chance, M.D. Wort, L.M. Miller, E.M. Scheuring, A. Xie, M. R. Chance)) Albert Einstein College of Medicine., Bronx, NY 10461. D.E. Sidelinger)) Albert Einstein Col of Med., Bronx, NY 10461 The binding of oxygen to hemoglobin and myoglobin is one of the most X-ray absorption spectroscopy (XAS) is unmatched in measuring metal-ligand important reactions in human cells. Essential to understanding the binding distances in solution while the dynamics of evolving systems is a subject of process is the study of intermediate states. To date, the intermediate states intense interest in biophysics currently. We report the design and successful involved in carbon monoxide binding are much better understood than those testing of a system for collecting time-resolved XAS data on a 5ps timescale. of oxygen binding. However, recent studies have shown that 02 and CO have The system is based on the use of a germanium energy resolving detector and significantly different rebinding intermediates (M. Chance, et. al., Biochemistry, a fast multichannel scaling (FMS) board, both from Canberra Ind. The output 29, 1990, p. 5537). Vibrational spectroscopic methods have indicated several of a single Ge channel is amplified and connected to the FMS board. The data bands for MbO2 ligand stretching modes (Potter, et. al., Biochemistry, 26, acquisition sequence is controlled by a digital delay generator, which also 1987, p. 4699). However, it is uncertain whether these bands correspond to controls the firing of a (doubled) Nd-YAG laser (output 100 mW, 532 nm, 10 various protein conformations, as they do for MbCO. If the multiple bands Hz). Software control allows the windowing of the x-ray fluorescence peak of have different rebinding kinetics, this supports multiple steric and electronic interest, which is then laid down in directly accessed memory with specifed environments of the distal histidine. time widths. A typical experiment laid down 8192 channels of data, each We present the results of low temperature recombination of 02 with myoolobin counting a 5 ps interval. For testing of the system, we used a well using Fourier Transform Infrared Spectroscopy (FTIR). The bound state of characterized chemical system, that of rebinding of carbon monoxide with oxymyoglobin exhibits three infrared bands of interest at 1090 cm', 1115 myoglobin after a laser flash at low-temperature. To date, we are aware of only cm', and 1 135 cm". Upon photolysis, the intensity of each band is reduced. one previous attempt to perform XAS in a time-resolved fashion on (300) ps After warming, the 02 and myoglobin recombine and the bands reappear. timescales ID. Mills, et. al., Science, 223, 1984, p. 811). In one experiment, Kinetic analysis of these bands helps to identify the presence of various protein an excellent x-ray edge was collected on 5pS timescales (4 mM MbCO, data conformations involved in the recombination process. Low-temperature collected every 4 eV, and 5000 sweeps at each energy). In a second recombination of samples at various pH's will demonstrate various protonation experiment, we demonstrated that with a 1 mM sample and 20 ps time states of the distal histidine. Also, we will present studies using isotopically resolution we could sit at a single x-ray wavelength, where the difference labelled 02 in order to identify those stretching modes directly related to the Fe- between the photolyzed and ligand bound spectra is the largest (kinetic 02 bond. This research is supported by a grant from the NIH, #HL-45892. spectrophotometry), and observe the photolysis and recombination of the sample. This work is supported by NIH grant HL-45892. M0Po109 M-PollO X-RAY ABSORPTION SPECTROSCOPY OF MBO AND MBCO REBINDING LIGAND CONCENTRATION DEPENDENCE OF THE REBIND- INTERMEDIATES. ((L.M. Miller, M.R. Chance M.D. Wirt, E.M. Scheuring)) Albert Einstein Col. ING RATE OF CO TO MYOGLOBIN. ((R. G. Philipp, R. M. Ernst, of Med., Bronx, NY 10461 G. U. Nienhaus, R. D. Young, H. Frauenfelder)) University of Illinois Recent studies have shown that MbO2 and MbCO have significantly different at Urbana-Champaign, Urbana, IL 61801.* rebinding intermediates. For example, the quantum yield of MbO2 photolysis at low temperature is 0.4 whereas that of MbCO is 1.0. X-ray absorption We compare the rate of rebinding of CO to myoglobin with the rate spectroscopy (XAS) can be used to study the differences between these two predicted for a bimolecular process. The measurements probe rebinding rebinding processes. XAS is especially sensitive to iron displacement from the kinetics in a glycerol/water solvent using flash photolysis over a wide heme plane and charge density on the iron atom. When a ligand is photolyzed from hemoglobin and myoglobin, the displacement and charge density of the range of time and temperature. We have used a pressure cell which Iron change, resulting in changes In the x-ray edge position and the XANES allows CO pressures of 0-200 atm, with a corresponding CO concentra- region of bound versus photolyzed hemoglobin or myoolobin. The x-ray tion which ranges from the low to high concentration limits. absorption spectrum of bound MbO2 was obtained at high resolution using 0.5 eV steps across the x-ray edge. First derivatives of the edge spectra are used 'This work supported by the Office of Naval Research. to accurately define the charge density on the central metal. The position of the MbO, edge can now be well defined at 7125.4 eV. In comparison, we find the x-ray edge position of MbCO to be at 7123.9 eV, indicating a significant difference in iron environments between the bound MbCO and MbO2. This result is consistent with studies that have shown a hydrogen bond between oxygen (but not CO) and the distal histidine of myoglobin. This hydrogen bond is stabilized by charge reorganization from the iron to the oxygen, resulting in a loss of charge density on the iron. This loss of charge density is reflected in the x-ray edge by a shift to higher energy. Additionally, we have collected x-ray edge and EXAFS spectra of photolyzed MbO2; both the x-ray edge and the XANES region show differences between the photolyzed and unphotolyzed MbO2.This work has been supported by NIH grant HL-45892. M-Poesll M-P0o112 A- AND B-STATE TRANSITIONS IN MYOGLOBIN ((K. Chu, J.R. INFRARED FLASH PHOTOLYSIS EXPERIMENTS ON THE TAXONOMIC Mourant, Y. Abadan, H. Frauenfelder, G.U. Nienhaus and R.D. Young)) SUBSTATES OF MYOGLOBIN ((Don C. Lamb, Bradley T. Banko, Hans Department of Physics, University of Illinois, 1110 W. Green St., Ur- ausn«feder, G. Ulrich Nienhaus and Robert D. Young)) Deatment of bana, IL 61801. Physics, University of Illinois at UrbanChampag, 1110 W. Green St., Ur- bana, Illinois 61801 FTIR spectroscopy on low temperature photoproducts of sperm Sperm whale carbonmaymyoglobin exhibits at least three spectroscop- whale carbonmonoxymyoglobin has revealed much information about icaily ditin able infrared stretch bands. They are Interpreted as three ligand rebinding dynamics in proteins. Several spectroscopic lines are different taxonomic substates,1 refered to as Ao, A1 and A3. Flash pho- observed around 1950 cm-' and 2150 cm-'; these are CO stretch bands tolysis piments have been performed on the Individual A substates by corresponding to conformational substates of the ligand bound (A sub- monitorng at slected wavelegths in the infrared The three temperature- states) and photolysed (B substates) protein-ligand system. The A and independent distnbutions of activation anthalpies for ligand rebinding after B substates undergo three separate classes of transitions following pho- photolysis, g(H), are detamined firom the low temperature kinetics (5OK - tolysis. Upon absorption of a visible photon by the heme, the ligand 160K) for the different A substates. Thes g(H) distributions are compared - heme bond breaks, resulting in an A-B transition. The resulting B for sample at different pH. The g(H) distributions are alao compared to those substates are not in thermal equilibrium and a B-RB exchange occurs. determined using teperature derivative spectroscopy. At temperatur above Finally, the ligand rebinds to the protein (B-_A). We use isothermal 180K, we describe the kinetics with temperature-dependent distributions of kinetics and temperature derivative spectroscopy to identify and char- rate coeffcients, f(A). The mexlmm entropy method was used to calculate acterize the tunneling and thermally activated transitions. (This work the f(A) for temperatures above 180K. The f(A) distributions provide addi- supported by the NSF and the NIH.) tlonal insight into the entrance and escape ofcarbon monouide from the heme pocket as wel as protein motins. This work is supported with grants from the NIH, the NSF and the ONR. 1H. Fafelder, S.G. SIgsa sad P.G. Wolyaes,Sc,mns254, 1559 (1991). HEMOGLOBIN AND MYOGLOBIN A43*AA M-Pos13 M-Posl14 MOLECULAR DYNAMICS SIMULATIONS OF LIGAND DISSOCIATION OXYGEN BINDING TO SINGLE CRYSTALS OF HEMOGLOBIN IN THE AND REBINDING IN MYOGLOBIN. ((Olivier Schaad, Huan-Xiang Zhou, T QUATERNARY STRUCTURE. ((A. Mozzarelli, C. Rivetti, G. L. Rossi, E. Eric R. Henry, Attila Szabo and William A. Eaton)) Laboratory of Chemical R. Henry, and W. A. Eaton)) Institute of Biochemical Sciences, University Physics, NIDDK, NIH, Bethesda, MD 20892 of Parma, and Laboratory of Chemical Physics, NIDDK, NIH, Bethesda, MD 20892. We have begun to study the kinetics of NO rebinding to myoglobin following photodissociation by molecular dynamics simulations. The Microspectrophotometry was used to measure reversible oxygen binding simulations included the complete protein molecule with all hydrogen atoms curves for single crystals of hemoglobin in the T quatemary structure.