Catalysts converted

Bioinorganic chemistry is an active new branch of chemistry concerned with how combinations of metal ions of different charges and sizes with the internal environments of protein molecules can be used by nature to carry out some crucial chemical reactions. These reactions are important in the processes of muscle contraction, DNA synthesis and replication, cellular signalling, hormonal response, nitrogen fixation, oxygen storage and transport, biosynthesis of amino acids, oxygen evolution in plants, and detoxification of harmful compounds in the human body, to name but a few. Proteins containing metal ions can be considered as sophisticated versions of coordination compounds first studied by Werner in the late 1800s.

Most new textbooks on bioinorganic chemistry are descriptive. This one is unusual in that its chapters are written by distinguished scientists actively involved in research in a particular topic. It is a textbook for advanced undergraduate and graduate courses. There are nine chapters, covering metal storage and transport, zinc chemistry, calcium chemistry, oxygen carriers, biological reactions involving oxygen, electron transfer, metal-sulphur proteins, metal/DNA interactions, and metals in medicine. All the chapters are written in the format of self-standing review articles, with extensive bibliographies.

The chapter on cellular metal storage and transport is excellent, although I would like to have seen discussions on the control of metal uptake, and the mechanisms of heavy metal resistance. There is one important aspect, which comes through very well when the structures of metal-containing proteins are discussed in detail at the atomic level, eg in the chapters on zinc, calcium, and the oxygen transport proteins such as haemoglobin. It is that nature encapsulates the metal in a cavity inside the protein, and lines the walls of the cavity with both hydrophobic (water-hating) and hydrophilic (water-loving) groups in close proximity of one another, and at strategic locations relative to the metal. These metalloproteins can therefore have exquisite specificities and selectivities. The tricks of the chemist are limited by comparison. This is not to say that the chemist cannot better nature in many ways: witness the huge successes of the chemical and pharmaceutical industries. An understanding of how nature builds catalysts to carry out some very difficult reactions so selectively under ambient conditions could help scientists to design new catalysts (or improve existing ones) which are more energy efficient, and hence more environmentally friendly.

Living organisms make use of the two major components, nitrogen and oxygen, of the earth's atmosphere. Nitrogen gas is transformed in the roots of plants to ammonia, and the oxidizing power of oxygen is much used in biosynthesis and in the breakdown of food to provide energy to sustain all aerobic organisms. Nitrogen fixation is catalysed by the nitrogenase enzyme system, which is discussed in the chapter on metal-sulphur proteins. Molybdenum was thought to be the key metal in this reaction, but the recent crystal structure suggested that it may be the iron that is involved in nitrogen fixation. We await further developments. The oxidizing power of oxygen is a double-edged sword because an unrestricted build-up of oxygen in cells can result in severe damage. The systems involved in the controlled, biological chemistry of oxygen are discussed in two chapters. The authors make valiant attempts at covering a vast area, and gaps are inevitable.

The transfer of electrons between protein molecules is a key reaction in biological systems, eg in photosynthesis, and the chapter on this topic is of the standard expected from one of the leading scientists in the field. The book is rounded off by an excellent chapter on metals in medicine, especially on the anti-cancer drug cis-platin.

This book is a valuable addition to the field; both the chemist and biochemist should read it in conjunction with standard biochemistry textbooks. There are criticisms, though. The bioinorganic chemistry of sodium, potassium and magnesium could have been discussed in a chapter, as could that of copper.

The factual details in some chapters obscure rather than clarify the issues. Where a concise summary of a class of enzymes or a topic is required, the book is found wanting. There could have been an introductory chapter, offering an overview of the link between the metal and proteins and the functioning of the organism, the reason the metals are chosen for their role, and most important, how a combination of "dead" systems (proteins, etc.) can lead to life.

Luet-Lok Wong is a lecturer in inorganic chemistry, University of Oxford.