Electron-paramagnetic-resonance spectroscopy in biochemistry: past, present and future.

Advances in instrumentation in a field of research usually spring from the collaboration between a scientist in that field and a physicist or engineer thoroughly familiar with the particular technique. Thus the beginnings of the application of e.p.r. in biochemistry can be mainly traced to the joint endeavours of such scientist pairs (occasionally triumvirates) in the 1950s, e.g. Townsend-Pake-Commoner, Blumberg--Peisach. Vinngard-Malmstrom, Vanngard-Bray or Sands-Beinert and their descendants. The deep and lasting influence that these physicist colleagues have had on the rapid and sound development of e.p.r. in our field can hardly be overestimated. The names of D.J.E. Ingram, J.F. Gibson, H . M . McConnell, J.D. Hyde and G. Feher must also be mentioned in this context. In the early 1950s the ground for the eager acceptance of a sensitive and specific technique for measuring magnetism was well prepared by earlier pioneering work in magnetochemistry, by measurements of magnetic susceptibility on haemoglobin by several groups (Coryell et al.. 1937; Scheler et al., 1956; Haveniann & Haberditzl, 1958) and on other haem proteins by Theorell & Ehrenberg (1952) and Theorell et al. (1952). by Michaelis’ work (195 1) on seniiquinones and his ideas on one-electron transfer and by the then emerging evidence that many enzymes, particularly those concerned with biological oxidations, contained transition metals as constituents (DeRenzo et al., 1953: Richert & Westerfeld, 1953, 1954; Mahler & Elowe. 1954; Kearney & Singer, 1955). The first report that I recall on the exploratory application of e.p.r. to biological questions appeared in Nature (Commoner et al., 1954) in 1954; but it took at least another 5 -10 years until work on biochemically welldefined systems was published, e.g. on purified enzymes such as peroxidases (Yamazaki et al., 1960), flavoproteins (Beinert & Hemmerich, 1965). metal flavoproteins (Rajagopalan et al., 1962. I’alnier et al., 1964) or copper proteins (Broman et al.. 1962; Blumberg et al., 1963). Very quickly specialintion set in with one faction rejecting e.p.r. in the frozen state as unphysiological, others turning to lowtemperature e.p.r. as required for the study of most metal proteins. Yet another faction branched off into free-radical chemistry specializing into radiation biology. spin labelling and spin trapping, while photosynthesis-e.p.r. straddled most of these areas. Even within the metal-e.p.r. field sub-specialization generated M o , Mn, V, haem, non-haem Fe and Cu specialists; and that is about where we stand today. Instrumentation, experimental approaches and knowhow.