Caveats about catalysis

The question that immediately comes to mind with this dictionary is: why is there no CD-Rom version? Dictionaries, given that one looks up only a particular short entry and other entries that correlate with the entry, gain facility in the CD-Rom format. (Of course, most people prefer to read longer documents on paper.) For example, when I was recently writing an article on abused drugs, it was necessary to compare the formulae, structures, physiological and medical properties of the principal substances contained in the drugs. It did not take long to search these out, but it would have been much quicker with a CD-Rom of this dictionary, which would also have given one the confidence that one had considered all the relevant material.

While it is true that the book's text is well strewn with cross-references, these would work even better in the CD-Rom format; and Oxford University Press has considerable experience and expertise in constructing such CD-Rom dictionaries.

It is customary for biochemists to claim that, naturally, all proteins and enzymes are important, none more so than the enzyme on which they are working. However, cytochrome c oxidase, which catalyses the conversion of molecular oxygen to water, really is important, in spite of the fact that I no longer work with it. Why, then, so little information on it here, and that incorrect, or at best, incomplete? I checked what is on the web and even I was surprised by the amount available.

Both mammalian and bacterial cytochrome c oxidases have had their structures determined, and to one such as this reviewer concerned with the role of metals in living processes, it is not unimportant that this enzyme contains two iron complexes, three coppers and one zinc, to say nothing of magnesium and calcium. If only the editors had made as much effort with this enzyme as they have with the enzymes responsible for the conversion of nitrogen to ammonia: a fascinating system, adequately described in the dictionary.

Of course, the use of molecular oxygen is not without risk in the sense that if the process of its conversion to water does not go exactly right, there is the risk that noxious species such as hydrogen peroxide may be formed, with damaging results. The precursor of the peroxide is thought to be the superoxide ion, formed from oxygen simply by the addition of one electron. Therefore the superoxide ion is effectively toxic, just as is one of the nastiest components of smoke, benz(a-)pyrene (not in the dictionary), which is the precursor of a really terrible carcinogen, its epoxide (in the dictionary).

Thus, the superoxide ion is effectively dangerous, but the brief description given in this dictionary gives the wrong impression of its toxicity. There is considerable evidence that the superoxide ion gives rise to the hydroxyl radical, yet the dictionary does not consider this, while it does remind the reader that the term hydroxyl radical was once - surely too long ago to be relevant - confusingly applied to the hydroxide anion.

I do not know whether to be pleased or sorry that techniques I am now using are not included in the dictionary. For example, scanning probe, scanning tunnelling and atomic force microscopies, which now play an important role in the investigation of biochemical, and even medical issues, are not mentioned.

The above caveats make one just a little wary of accepting unquestioningly the descriptions offered in this dictionary. Nevertheless, it is a valuable reference source and should be widely available to every biochemist and molecular biologist while we await the (imminent?) arrival of its CD-Rom version.

H. A. O. Hill is professor of bioinorganic chemistry, University of Oxford.