In the preface to the Second edition, we made a prediction that many exciting developments would take place in the coming years that would change the face of a new edition. This has indeed been the case and the current edition reflects these new advances. Our picture of the structure of the fatty acid synthetase has changed dramatically, bringing a new concept in enzymology - the multicatalytic polypeptide chain. This new knowledge owes much to the exploitation of genetic mutants, the use of which is undoubtedly going to extend into many other areas of lipid biochemistry. An understanding of the control of lipid metabolism has also advanced considerably during the last decade and we have tried to reflect that here, although it will be some years before a truly integrated picture can be obtained. For this reason we have continued to deal with the control of particular aspects of lipid metabolism - fatty acids, triacylglycerols, lipoprotein- in the specific chapters but we can foresee the time when a chapter on the overall integration of lipid metabolism will be appropriate and feasible. As a particular example, the exciting new concepts of the control of cholesterol metabolism in specific tissues via the interaction of low density lipoproteins with cell surface receptors have been described in Chapter 6.

Lipids can usually be extracted easily from tissues by making use of their hydrophobic characteristics. However, such extractions yield a complex mixture of different lipid classes which have to be purified further for quantitative analysis. Moreover, the crude lipid extract will be contami nated by other hydrophobic molecules, e.g. by intrinsic membrane proteins. Of the various types of separation processes, thin layer and column chromatography are most useful for intact lipids. High performance liquid chromatography (HPLC) is also rapidly becoming more popular, especially for the fractionation of molecular species of a given lipid class. The most powerful tool for quantitation of the majority of lipids is gas liquid chromatography (GLC). The method is very sensitive and, if adapted with capillary columns, can provide information with regard to such subtle features as the position or configuration of substitutions along acyl chains. By coupling GLC or HPLC to a radioactivity detector, then the techniques are also very useful for metabolic measurements. Although research laboratories use generally sophisticated analytical methods such as GLC to analyse and quantify lipid samples, chemical derivatie: ations are often used in hospitals. For these methods, the lipid samples are derivatized to yield a product which can be measured simply and accurately-usually by colour. Thus, total triacylglycerol, cholesterol or phospholipid-phosphorus can be quantitated conveniently without bothering with the extra information of molecular species, etc. which might be determined by more thorough analyses. REFERENCES Christie, w.w. (1982) Lipid Analysis, 2nd edn, Pergamon Press, Oxford."