Only fifty years ago the role of metal ions in living systems was hardly treated seriously in biochemical textbooks or indeed in biochemical research with the exception of the strongly pigmented cofactors -heme (Fe) and chloropyll (Mg). Between 1950 and 1970 there was a slow awakening to the fact that apart from the conventional non-metal elements H, C, N O, S and P, there were essential metals in addition to Fe and Mg including Na, K, Ca, V, Mn, Co, Ni, Cu, Zn, Mo and W. (In passing, note that at the same time the number of non-metals essential in many, if not all, organisms, increased to include B, Si, Se, I and perhaps Cl). There has followed an intensive study of all these elements which demands not only a broad-brush treatments as appears in books on biological inorganic (or bioinorganic) chemistry, but also a source or handbook to which one can turn for the detailed knowledge of individual molecular species. Just as the task of supplying a handbook of all organic species found in cells or even one restricted to all proteins in cells is an impossible task, so it is not possible to provide a handbook of all metal-containing proteins. The Editors have therefore made two decisions: (i) to limit the elements analysed to metals firmly attached to proteins, hence eliminating the elements, Na, K, Mg and Ca; (ii) to exclude Zn which today merits a handbook on its own. What this handbook contains is then a description of the major proteins of mainly transition metal elements, through reference is made to magnesium in chlorophyll.

Very wisely the Editors have asked each contributor to the more than 100 separate entities to concentrate upon structures. However, in each article authors have put the structural data to full use in the description of binding sites of substrates and in the discussion of activity when dealing with enzymes. Of course, a fair proportion of metalloproteins have other functions, in, for example, metal transport, gene activation, sensors and carriers. All the major examples of these functionally important proteins have been included. The reader will also find that for each protein there is a systematic descriptive section on functional class, occurrence, biological function, amino-acid sequence, protein production and purification, metal content and cofactors, activity tests and spectral properties before the extensive descriptions of structure, including crystallisation details, and then, the activities form the major sections of each chapter. Note that the requirement that a structure is available has meant that there still remains a large number of proteins which could not be included.

It is my opinion in the light of experience that the inclusion of a more speculative analysis of function in the absence of structure would have been detrimental to the extremely high demands which the Editors have put upon their contributors. This handbook therefore provides a safe and comprehensive foundation based on molecular biological information on which the future discussion of cellular activity of metals has to be based.

R.J.P. Williams
January 2001

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Table of Contents and Contributors
Foreword