Fisiologia vegetal

Fisiologia vegetal

BIOCHEMICAL EDUCATION July 1976 Biochemistry of Carbohydrates Two chapters following this are concerned with connective tissue proteoglycans - - th...

278KB Sizes 0 Downloads 60 Views

BIOCHEMICAL EDUCATION

July 1976

Biochemistry of Carbohydrates

Two chapters following this are concerned with connective tissue proteoglycans - - their biosynthesis described by L. Roden & N. B. Schwartz and their structures and properties by Helen Muir & T. E. Hardingham. As the Editor points out in his Preface, this is a field where advances in methodology have at last made possible a much closer understanding of these complex molecules and their probable functions: 'which include situations where carbohydrates are seen to carry and transmit information in as clear a fashion as the genetic code.' These two chapters together occupy almost one third of the volume, but the authors are to be congratulated on such a clear exposition of a difficult subject. The Regulation of Intermediary Carbohydrate Metabolism, an excellent chapter by M. G. Clark & H. A. Lardy, follows. Although a highly compressed account of a subject about which volumes have already been written, the authors have succeeded in presenting a remarkably complete synopsis of the main features, filling to some extent a gap in the remaining sections of the book, in that it traces step-by-step the enzymic regulatory mechanisms starting with the glucose molecule. (The metabolism of glycogen is the subject of another chapter.) Dietary and hormonal factors are not so much considered as the regulatory effects of isoenzyme and allosteric forms and modification of them by interaction with other enzymes, substrates, cofactors, phosphorylation and dephosphorylation; all very well brought out. The Chemistry and Biochemistry of Starch is excellently surveyed by D. French in a highly readable account of which the first half is chemical and physical, the latter half enzymic and metabolic, relating to animals, plants and micro-organisms. It is interesting that the role, if any, of phosphorylase in plant biosynthesis is still considered enigmatic, in spite of the 36 years since its discovery in peas and potatoes by Hanes. A very satisfying review by E. G. Krebs & J. Preiss follows, covering Regulatory Mechanisms in Glycogen Metabolism, in animal tissues and in micro-organisms. The authors distinguish between potential regulatory mechanisms arising from the enzymologists' studies in vitro and those which probably take control in specific physiological situations. Again, allosteric forms and interconversion of enzymes, e.g. of phosphorylases a and b, are fully dealt with, and endocrine and genetic aspects are not overlooked. The final chapter, some Inborn Errors of Carbohydrate Metabolism, by D. H. Brown & Barbara I. Brown, is admittedly highly selective in its choice of recent subjects for review: 'many other diseases of equal importance, such as galactosemia, have not been mentioned'. Instead, glycogen storage diseases, errors of fructose metabolism, and the technically difficult field of giycosaminoglycan (acid mucopolysaccharide) metabolism receive full and valuable new treatment. In the last mentioned, modern techniques using cultures of fibroblasts from patients are not only revealing more of these disorders, but also shedding new light on the catabolic pathways existing for these materials, hitherto very obscure. As a member of this Series, 'designed to provide a comprehensive, critical and continuing survey of progress in research', the present volume lives up to this high standard, and will be warmly welcomed. F. Dickens. 15 Hazelhurst Crescent Findon Valley Worthing, England.

E d i t e d by W. J. W h e l a n . 1975, p p 441. Medical a n d Technical P u b l i s h i n g Co. I n t e r n a t i o n a l Review of Science: Biochemistry Series 1, Vol. 5. P u b l i s h e d by B u t t e r w o r t h & Co. Ltd., L o n d o n , U . K . a n d University P a r k Press, Baltimore, U . A . A . Price £10.45. Although the title of this book might suggest at first sight that it is a general text-book of carbohydrate biochemistry, it is in fact a collection of eight fairly long (35-70 pp.) essays on carefully selected topics coming under this overall heading, making no claim to be comprehensive but, in accordance with the planning of this new Series of twelve volumes entitled Biochemistry Series One, laying great emphasis on aspects where recent progress appears to be greatest. The editorship of this volume, together with the series consultant editorship of H. L. Kornberg and D. C. Phillips, has on the whole achieved this difficult aim very successfully, though in his Preface the volume editor admits to bias in selection of subjjcts, while maintaining that carbohydrates are quite the most important of biological molecules, beginning from the standpoint that the nucleic acids are substituted polysaccharides.' Apart from stretching the usual definition a good deal, this statement is perhaps slightly irrelevant, since the nucleic acids are not discussed here but in Vol. 6 of the present Series under the editorship of K. Burton. For the contents of this book and the way in which it has developed its purpose of indicating in some detail the main directions of current research in this field, there can be nothing but praise. The choice of contributors is a very happy one, all of them being active and leading research workers as well as having the gift of clear exposition. The book is also very well produced and most chapters are well illustrated, and all have quite full and up-to-date bibliographies. There is a subject index which is reasonably comprehensive. The price, especially that of the whole collection, i s daunting; so an attempt will be made here to outline the main contents as a guide to intending purchasers of this volume. It should be noted at the outset that emphasis is strongly on the mammalian polysaccharides; indeed only one of the eight chapters (that by Clark and Lardy) is devoted to simple sugars and their metabolic control. The opening chapter, by D. A. Rees, is noteworthy for developing an original viewpoint on the stereochemistry and binding behaviour of various types of carbohydrate chains, including binding to noncarbohydrate materials, and its relation to biological function. It is suggested that the finer points of structure need to be studied as far as possible on these substances in their native state, when it appears likely that while their inter-relationships are less involved than those of say proteins or nucleic acids, they nevertheless contain more fine detail having biological significance than we have hitherto appreciated. It is worth mentioning that the series of stereo-pairs, based partly on diffraction evidence, showing some known configurations of alternating copolysaccharide helices (Fig. 1.1), require a special stereoviewer as they are in black and white. The model recommended is from U.S.A., but the reviewer obtained reasonable results with a normal type of stereoviewer as used for viewing miniature camera transparencies. This is a valuable basic chapter and one that breaks new ground. Next, K. W. Talmadge and M. M. Burger discuss in detail Carbohydrates and Cell-surface Phenomena. As is well-known, mammalian cell surfaces, unlike those rigid walls of microorganisms and plants, possess mucopolysaccharide and glycoprotein or glycolipid components as essential elements. The structure and metabolism of these compounds is well described, followed by an account of their origins and possible functions in a wide variety of cell types, including virns-transformed cells. Recent promising work on lectins as tools for the study of cell surfaces, on surface antigens for revealing the organization of cellular membranes, and on the role of surface carbohydrates in cellular recognition processes is concisely described. These properties and intercellular adhesion phenomena are related to the probable underlying enzymic basis, a fascinating recent development.

Vol. 4

No. 3

59

Fislologia Vegetal Carlos V i n c e n t e C o r d o b a . P p 440. H. B l u m e ediciones, M a d r i d . 1976. P a p e r b a c k , 1,000 pesetas. (Text in Spanish.) This book aims to present the student of biology with an account of our current knowledge of the physiology of the higher plants. The author has planned his text around the changes occurring during the complete life cycle of the plant; thus the early part of the book deals with the process of germination of the seed and follows the events of growth and differentiation. The main sections of the book

60

BIOCHEMICAL EDUCATION

describe the activities of the adult plant and are followed by a description of the hormonal control of ageing and the eventual death of the plant. The approach adopted by the author as outlined above is successful but is marred by being rather dated, particularly in those sections covering the biochemical aspects of the plant's life cycle. The section on electron transport for example has nothing to say of the chemiosmotic theory and similar criticism can be made of the descriptions of photosynthesis - - the references to both these sections and to most others have few entries which are more recent than the mid 1960's. The other serious criticism is that there is no detailed discussion at any point in the book of the nature and role of the cell membrane. Transport, water and ion movements, photosynthesis and oxidative phosphorylation are all membrane mediated processes and any discussion of the physiology and biochemistry of such processes must consider the vital role played by the various membranes of the plant cell. A more modern version of the book which retains the same overall plan would be most welcome. G. G. Lunt Department of Biochemistry University of Bath Bath BA2 7AY, U.K.

The Cell in Medical Science. Volume 1: The Cell and its Organdies Edited by Felix Beck a n d John B. Lloyd. A c a d e m i c Press, London & New York, 1974. Pp 366. £7.80 a n d $20.25. Cell biology is an exciting field, and, quite unlike the situation ten to fifteen years ago, a remarkably varied group of people would now claim to be cell biologists. Biochemists no longer inhabit a space free world, and they, and molecular biologists, are looking for new pastures. The real reason for the intense interest in cell biology was pointed out a few years ago by Francis Crick: the ratio of how much is known in cell biology at present to how much is still to be learned is very small, whereas with biochemistry or molecular biology, the ratio is much larger. So cell biology is expanding and changing rapidly and for medical teachers and students this presents some problems, for this rate of change is far greater than in any other subject. Last year's, or at least the last few years', lecture notes will no longer do. More important, the students are confronted very forcibly with a field in which definite answers cannot be given to major questions and uncertainty is commonplace. Take such central problems as control of cell division, or cell differentiation, or cell movement, and we can offer interesting ideas and experiments but emphasis must be on our ignorance. Medical students on the whole do not like this, for, being very rational, they want to know what they must remember and always with their eye on clinical relevance, they find such uncertainty unhelpful and displeasing. One tries with varying degrees of success to compensate for this by emphasizing the importance and intellectual challenge of the topic. There are also other problems. What is cell biology anyhow? Where does it begin and biochemistry end? Are we not all cell biologists now? How nice it would be to have a book which helped one with these difficulties. The present volume does not. This volume is on the cell and its organelles. It has very competent chapters on membranes and transport (Lucy), the cell surface (Moores & Partridge), nucleus (Mathias), cytomembranes and ribosomes (Campbell & yon der Decken), mitochondria and peroxisomes (Baum), Lysosomes (Lloyd & Beck), and snbcellular pathology (Allison). They could however be chapters in any of the dozens of books or reviews on cell biology. Some are very biochemical, some are not. They are neither stimulating, nor very up to date. They do not link with one another or make any particular effort to be relevant to medicine. The single exception to these criticisms is the stimulating article by Allison on subcellular pathology. Lewis Wolpert Dept. of Biology as applied to Medicine The Middlesex Hospital Medical School London WlP 6DB.

July 1976

Vol. 4

No. 3

Biochimie. Etudes m&lieales et Biologiques By Jacques K r u h . 3rd Edition, 1975. H e r m a n n , Paris. Pp 519. 220 x 150 m m , p a p e r b a c k , in French. The author is one of the Professors of Biochemistry in the Faculty of Medicine, Cochin-Port Royal of the University of Paris V. The book is intended for students of medicine and biology in the first two years (premier cycle) of their university studies. The book is divided into seven main sections, the first of which is an introductory one dealing with the characteristics of biochemical reactions, the general methodology of biochemistry and the principal techniques in use today. In the second section the chemical and physical properties of simple biochemical compounds - - sugars, lipids, amino acids, and purine and pyrimidine bases - - are described. This occupies some 50 pages, it is very 'chemical' and does not attempt to put the various substances considered into any 'biological' perspective. Then follows the largest section, occupying 160 pages, devoted to informational macromolecules. It deals with the chemistry and physical chemistry of proteins, including enzymes, and the nucleic acids. The processes of protein synthesis are dealt with extensively. This part contains a great deal of information and is clearly and interestingly written. Oxidations and the pathways of degradation of sugars, lipids and amino acids for the production of useful energy are described in the fourth section. Then follows an account of the storage of energy as polysaccharides and trigiycerides and of the ways in which this potential energy can be mobilized. Included in this section is a short and superficial account of photosynthesis. These two "metabolic' parts extend over some 125 pages. The next 75 pages contain descriptions of the biosynthesis and metabolism of a rag bag of important compounds that have not found a place in earlier chapters. These include mucopolysaccharides, sphingolipids, sterols and steroids, some amino acids, nucleotides, vitamin A, and haemoglobin. The last 22 pages are devoted to the regulation of biochemical processes. Ten functions of cyclic AMP are listed and some of the effects of hormones are mentioned. There are a number of fashionable diagrams in this section with different kinds of arrows showing positive and negative regulatory effects. The most fantastic of these is supposed to show the principal regulations of metabolism, it contains 18 arrows indicating activation of 7 for inhibition emanating from 7 boxes labelled insulin, glucagon, ATP, etc. and pointing to some half dozen metabolic pathways. On the positive side, the printing is good and the look of the pages is pleasing. The diagrams and formulae are clear and the judicious use of red printing is helpful. The text is lucid and easy to read. There are a few annoyances such as the gas constant being given incorrectly in kilocalories per mole degree on page 268, while on page 275 it is given correctly in joules per mole degree. On the other hand there are a number of surprizing omissions. Thus, while a whole quiverfull of arrows is used to show the actions of insulin and glucagan on metabolism, nowhere are we told how the secretion of these hormones is controlled. The ketone bodies are only briefly mentioned and there is no discussion of their importance in the utilization of fatty acids at times of carbohydrate shortage. There is hardly any discussion of the different metabolic properties of different organs and tissues. In truth, the book throws an enormous number of facts at the reader with very little to help him to put them into perspective in relation to the functioning of the organism as a whole. This is a disappointment. Finally it should be said that, while no references are given in the text, there is an appendix that lists a number of general and particular reference works. There is a list of the principal journals in which original biochemical research is published and the existence of FEBS and its annual meetings and IUB and its triennial congresses are mentioned. S. P. Datta Department of Biochemistry University College of London Gower Street, London WC1E 6BT.