Throwing light on photosynthesis

Throwing light on

photosynthesis

Molecular mechanisms of photosynthesis

by Robert E. Blankenship, BlackwellScience, 2002. US$49.95/£29.95 (352 pages)ISBN 0 632 04321 0

It has long beenknown that lightcan be convertedinto usefulchemical energy.The importance ofthis photosyntheticprocess has beenrecognized indifferent waysthroughout history,

and was elegantly acknowledged byJulius Robert Mayer in 1845 when hewrote: ‘Nature set herself the task ofcapturing the light flooding towards theearth and storing this, the most elusive ofall forces, by converting it into animmobile force…the plant worldconstitutes a reservoir in which thefleeting sun rays are fixed and ingeniouslystored for future use, a providentialmeasure to which the very existence of thehuman race is inescapably bound’.

In his recently published book,Bob Blankenship replaces Mayer’sflowery definition of photosynthesis with‘a process in which light energy iscaptured and stored by an organism andthe stored energy is used to drive cellularprocesses’. Behind this simple and ratherbland modern definition of photosynthesislies a vast base of knowledge,encompassing disciplines ranging fromphotophysics and photochemistry tomolecular biology and physiology. Thereactions of photosynthesis are initiatedby the absorption of quanta by pigments,which occurs in the femtosecond timedomain, followed by reactions thatproceed in a time-scale stretching to daysor even years. Therefore, to write acomprehensive text book on the molecularmechanisms of photosynthesis is adaunting task. Blankenship has taken upthis challenge and, in my view, hasproduced a first class product. Hisapproach is sensitive to the student readerand, with this in mind, he has included a

47-page appendix in which theappropriate basic principles ofphotophysics are well described.The remaining 257 pages comprise11 chapters, in which Blakenship leadsthe reader through a logical progression ofphotosynthesis. The first three chaptersset the scene, giving basic concepts interms of reactions, where they take placeand how they were discovered. Thisfoundation is then built upon with athorough coverage of structural andspectral properties of the photosyntheticpigments, and of the means by which theyare associated with proteins. Over thepast few years, X-ray crystallography hasprovided spectacular insights into howthese pigment proteins are arranged, andhas also given a structural basis toexperimental and theoreticalconsiderations of the energy transfermechanisms. All this is dealt withrigorously by Blankenship. His account ofreaction centre complexes in Chapter 6deserves equal praise. He could not bemore up-to-date in his content, providingthe reader, for example, with a discussionof the latest X-ray structures ofphotosystems (PS) I and II. Chapter 7 is abit of a hodgepodge. Quite rightly,Blankenship moves on to othercomponents of the photosynthetic electrontransport chain. He gives details of thesimilarities of the bacterial cytochrome bcand chloroplast cytochrome b6f complexes,and discusses the role of diffusable redoxcofactors such as plastoquinone,plastocyanin, ferredoxin and NADPH.However, the discussion of turnover of theD1 protein of PSII and chlorophyllfluorescence as a probe of PSII functionseems, to me, to be misplaced inthis chapter.

The conversion of ADP to ATP, the roleof proton gradients, and Mitchell’schemiosmotic hypothesis are detailed in auseful and readable way in Chapter 8. In addition, this chapter focuses onspeculations about the rotatory ATPsynthase mechanism by drawing on themost recent structural informationavailable.

It has been traditional to consider theprocesses of photosynthesis as consistingof two stages: light and dark reactions.Blankenship has continued this traditionand uses Chapter 9 to discuss biochemicaldetails of the dark reactions; namely

carbon fixation via C3, C4 and CAMmetabolism. He also includes the CO2concentrating mechanism found inaquatic photosynthetic systems, and thebiochemical reactions involved in long-term storage of photosynthate as sucroseand starch.

The photosynthetic apparatus,whether it be of anaerobic bacteria oraerobic cyanobacteria, algae and higherplants, is complicated, being composed ofmany hundreds of different proteins,enzymes and cofactors. How thesecomplex systems assemble themselvesand how they evolved are the subjects ofthe last two chapters, respectively.Blankenship has a keen interest in theevolution of photosynthesis and hischapter on this subject makes goodreading. Although there are major gaps inour knowledge, recent advances in genesequencing and structural analyses ofphotosynthetic proteins are providingfodder for fascinating and realistichypotheses; these provide a grand finalefor this excellent text book. I will have nohesitation in recommending it to mystudents and colleagues alike.

James Barber

Ernst Chain Professor of Biochemistry,Dept of Biological Sciences, Imperial Collegeof Science Technology & Medicine, London,SW7 2AY, UKe-mail: j.barber@ic.ac .uk

Microarray data

analysis for dummies ……and experts too?

Microarray Data Analysis and Visualization

edited by Arun JagotaBioinformatics By The Bay Press, 2001.US $29.95 (101 pages) ISBN 097002973X

When I first encountered microarraytechnology back in 1999, I was fascinatedby its revolutionary role in aiding ourunderstanding of complex biologicalsystems and by its immense potential forthe post-genomics era. I started to read asmany references on this technology aspossible and was soon startled by myunfamiliarity of the data analysisdescribed by a few key publications. I was

TRENDS in Biochemical Sciences Vol.27 No.8 August 2002

http://tibs.trends.com 0968-0004/02/$ – see front matter © 2002 Elsevier Science Ltd. All rights reserved.

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