3) This paper as originally submitted to the Editor cited more than 100 references, which occupied fully one-third of the paper. In order to meet the space criteria of Accounts, we have chosen, where possible, to cite only recent references. A recent monograph gives an excellent up-to-date review of many areas touched upon here. Cytochrome P-450: Structure, Mechanism and Biochemistry, 2nd ed.; Ortiz de Montellano, P. R., Ed.; Plenum Press: New York, 1995. (4) Even the trivial names of porphyrins are frequently complex. In this review the major porphyrins are abbreviated as follows: TPP ) mesotetraphenylporphyrin (2a) etc. as shown for structures 2-14.Teddy G. Traylor (1925Traylor ( -1993 never graduated from high school, but after the war, where he served in the Merchant Marine, he received his Ph.D. at UCLA with Saul Winstein and then was a postdoctoral fellow with Paul Bartlett at Harvard. He was the first organic chemist hired at UCSD, where he was a pioneer in organometallic chemistry. Teddy was the first to publish papers on superstructured porphyrins, and his research on oxygen binding and P-450 chemistry was seminal for the past two decades. His love of chemistry was surpassed only by his love of life. We are sorry that he is not with us to still enjoy them. David Dolphin was born in London, England, at the beginning of the Second World War. After obtaining his undergraduate and graduate degrees at the University of Nottingham, he was a postdoctoral fellow with R. B. Woodward at Harvard and then joined the faculty there in 1966. In 1973 he joined the University of British Columbia, where he has been acting Dean of Science and is the NSERC/ QLT Industrial Research Professor in Photodynamic Technology. He is also the V.P. of Technology Development at QLT PhotoTherapeutics, a Vancouver-based biotechnology company that is the world leader in photodynamic therapy. Lily Y. Xie was born in Chongqing, People's Republic of China. She received her B.Sc. degree at Peking University in 1983 and her Ph.D. in 1990 at the University of British Columbia (UBC) under the direction of Brian R. James. She worked as a postdoctoral fellow with David Dolphin at UBC and then with Alison Butler at the

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Rates for the reaction of nitric oxide with several ferric heme proteins and model compounds have been measured. The NO combination rates are markedly affected by the presence or absence of distal histidine. Elephant myoglobin in which the E7 distal histidine has been replaced by glutamine reacts with NO 500-1000 times faster than do the native hemoglobins or myoglobins. By contrast, there is no difference in the CO combination rate constants of sperm whale and elephant myoglobins. Studies on ferric model compounds for the R and T states of hemoglobin indicate that their NO combination rate constants are similar to those observed for the combination of CO with the corresponding ferro derivatives. The last observation suggests that the presence of an axial water molecule at the ligand binding site of ferric hemoglobin A prevents it from exhibiting significant cooperativity in its reactions with NO.

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The rates of binding of carbon monoxide and imidazoles to ferrous hemes are reported. By flash photolysis of appropriate heme(CO)(Im) mixtures it is possible to determine all ten rate constants relating the five species heme, heme(CO), heme(Im), heme(Im)2, and heme(CO)(Im). Under all conditions, some of the return from heme(Im) to heme(CO)(Im) proceeds via loss of imidazole, followed by addition of CO and subsequent addition of imidazole, the "base-elimination" pathway. Both benzene and aqueous detergent (cetyltrimethylammonium bromide) have been used as solvents; the similarities and differences are discussed. The rates of the heme-CO-imidazole mixtures are compared with those found in heme proteins. The sterically hindered 2-methylimidazole serves as a model for T-state hemoglobin, while the unhindered imidazole or 1-methylimidazole serves as a model for R-state hemoglobin.

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