74 BIOCHEMICAL EDUCATION October 1975 Vol. 3 No. 4

BOOK REVIEWS

chemistry By Linus Paul@ and Peter Pauling (1975). XVI + 767

pages, price $13.95. W. H. Freeman &Co., San Francisco.

The scope of this book is similar to that of General Chemistry by Linus Pauling, 3rd edition, 1970. Changes have been made in presentation and content, and these are explained when prefaces are compared. General Chemisrry was designed “for use by first- year college university students who plan to major in chemistry or in closely related fields” whereas the present book is designed for students “primarily interested in biology, medicine, human nutrition, and related fields”. The former book was longer by about 200 pages, and several topics are treated less rigorously as, for example, those that involve discussions of quantum and statistical mechanics, and chemical thermodynamics. However, atomic structure and the periodic table, the nature of chemical bonds, basic inorganic chemistry - especially that of coordination compounds, properties of solutions, chemical equilibria and other subjects are discussed with the competence and clarity that assured the success of Genercrl cherntirry for more than 20 years. An understanding of these topics is a necessary foundation for a biochemical education, and the present book is recommended for this purpose. Of special interest to biochemists is the replacement of one section on biochemistry by two chapters on biochemistry and molecular biology. The second of these is an excellent, brief intro- duction to the subject. However, I am far from enthusiastic about the section &voted to biochemistry, although I realize that anyone who sets out to introduce this subject within the confines of 50 pages must exercise a rigorous selection of material and will therefore satisfy few critics.

Early in this chapter the question is posed as to what features distinguish a living organism from an inanimate object, and the difficulties of defining the word ‘living’ are then discussed. My own inclination would have been to develop this theme in a different direction. I would have preferred to stress the dynamic chemical state of living matter (so different from the isolated systems of inanimate nature studied by students in chemistry courses) with metabolism operating through an inter-woven network of reaction sequences, with synthetic and degradative pathways separated, and each controlled by ‘automatic’ regulatory mechanisms, and with constancy of macromolecular design guaranteed throughout this complicated flux of material by continual reference to ‘automati- cally’ perpetuated sequences of nucleotides present in DNA and RNA. By contrast, this book introduces students to biochemistry through chemical structures of amino acids and proteins, poly- saccharides, lipids, vitamins and hormones. Their biological significance is brought out by describing their importance for health: thus essential amino acids are listed and the pioneering work of W. C. Rose is described. Ways of reducing cholesterol levels and avoiding the common cold are discussed, recommended dietary allowances for male adults are listed, and there is a section on chemistry as it relates to medicine. How far it deviates from my personal preferences is seen by the omission of any references to glycolysis or pyruvic acid. However, there are brief sections on photosynthesis and the citric acid cycle where it is stated that “citric acid is converted to a four-carbon dicarboxylic acid by a series of six steps, in two of which carbon dioxide is released. The four-carbon acid is converted to oxaloacetic acid in three additional steps. All of these steps are catalyzed by specific enzymes, and in each of several of them a high-energy molecule is produced.” Details of the cycle are given in a diagram, in which pairs of hydrogens are seen to be removed in the oxidation of isocitrate and succinate but not at other points. There is no mention of the fate of these hydrogens, nor of the origin of acetyl CoA which is oxidized by the cycle. Although pyruvic acid is not mentioned, an opportunity for indicating how the Krebs cycle is related to other processes would have been

provided in the section on lipids; however, it is stated there that “fats are oxidized (catabolixed) in the body by splitting off two carbon atoms as acetic acid and forming a shorter chain”. I also

feel that the metabolic significance of thiamine and pyridoxine would have been broadened by reference to the coenxymic functions of the appropriate phosphotylated derivatives. Thus, it is stated that “thiamine appears to be important for metabolic processes in the cells of the body. but the exact way in which it operates is not known. There is some evidence that it is the prosthetic group for an enzyme involved in the oxidation of carbohydrates”. The evidence is, indeed, strong that thiamine as its pyrophosphate serves as co- factor for enzymes that catalyze the decarboxylations of cl-keto acids, and also for benzoin-type condensations such as occur in the pentose-phosphate cycle. The analogy between the catalytic properties of thiamine pyrophosphate in biochemistry, and the cyanide ion as used as a catalyst by organic chemists, has often been mentioned ever since R. Breslow discovered in 1957 that the hydrogen atom at C-2 of the thiaxolium ring readily exchanges with solvent deuterium. It is stated that “pyridoxine and its derivatives serve as coenxymes for scores of enzyme systems” but the student (and this reviewer) would be assisted if some examples were given.

The terminology ‘energy-rich molecule’ is discussed on page 258, but I believe some students might be confused by describing the decomposition of hydraxine, and its use as a rocket fuel, alongside the energy-rich character of ATP. For the former reaction it is calculated that replacement of N-N bonds in hydrezine by N-N bonds in nitrogen gas results in the liberation of 469 kJ mole * when hydraxine explodes. For the hydrolysis of ATP (giving ADP) the standard free energy change has been estimated (1) to be about 29 kJ mole I, and of course in biological systems ATP is not hydrolyzed under standard conditions. I must stress that ATP is not described as a fuel in this book, although this term has been used by other authors who are more prone to explain metabolism by homely analogies. Since ATP is hydrolyzed rather than detonated, I believe that a better parallel is provided by considering the reaction of acetyl chloride with water and contrasting its behaviour with that of methyl chloride. But I think we already have more than enough energy-rich compounds without adding organic chemical reagents. If you take four biochemicals (Dr. Barbara Banks (1) listed five more) namely glycerol l-phosphate, glucose l-phosphate, ATP and phosphoenolpyruvate, and then write down their relative standard free energies of hydrolysis you obtain the approximate ratios 1.0:2.2:3.0:5.6. A traditional biochemical education gives one the necessary confidence to divide the rich from the poor at a point between the second id third numbers. This expertise is useful since most energy-poor metabolites are richer than glycerol I- phosphate, and most of the rich are less affluent than phosphoenol- pyruvate. These categories, like stable societies, are firmly based upon a solid middle class.

Note:

Stanley Dagley

(1) Values taken from an article in Chemistry in Britain vol. 5

(1969) 514 by B. E. C. Banks who makes a similar point about

energy-rich phraseology. Activities of reactants and products were

set at unity, except for the hydrogen ion (lo-‘); and magnesium

ions (0.01 M) were added to hydrolysis mixtures.

Collected Tentative Rules and Recommendations of the Commission on Biochemical Nomenclature (IUPAC-IUB) 2nd edit@. 1975. Pp 150 paperback. Obtained from the American Society of Biological Chemists, Inc. 9650 Rock- ville Pike, Bethesda, Maryland 20014, U.S.A. $3.00 per copy, but 20% discount on 10 + copies. Postage included, remittance in U.S. % with order.

This compilation of all tentative rules and recommendations published up to May 1975 and edited only to eliminate superceded sections is now available.