Chairman's Opening Remarks 



T. W. GooDwix 



Department of Agricultural Biochemistry, University of Wales, 

 Aberystwyth, Wales 



A glance at the list of distinguished speakers in today's proceedings 

 quickly made me realize that it would be an act of supererogation if I 

 attempted to discuss chloroplasts and chromatophores in general terms as 

 an introduction to the session. I feel that it would be much more profitable 

 if I made some general observations on one member of those inseparable 

 photosynthetic twins — the carotenoids and the chlorophylls. Dr. Smith 

 will discuss certain aspects of chlorophyll biochemistry, so I shall confine 

 myself to the carotenoids. The invariable co-existence of carotenoids and 

 chlorophylls in all photosynthetically active units strongly indicates an 

 important function of carotenoids in photosynthesis. It has been known 

 for a long time that they play an ancillary role in photosynthesis ; they 

 absorb light in the region of the spectrum least efl^ectively used bv chloro- 

 phyll and pass it on, with \arying degrees of efficiency in different 

 organisms, to chlorophyll for use in the primary photosynthetic act. This, 

 however, does not make the carotenoids essential to photosynthesis, but 

 only allows the more efficient use of the energy of the visible spectrum. 

 However, the invariable association of carotenoids and chlorophylls in 

 photosynthetic organisms suggests a more fundamental role than this. As 

 Stanier [i] has put it, "In the long run natural selection ruthlessly 

 eliminates non-functional gadgetry from living organisms and as biologists 

 we may therefore be fully confident that the carotenoids of the photo- 

 synthetic apparatus are not merely the organic equivalent of tail fins". 

 The work of Stanier and others strongly indicates that the essential func- 

 tion of carotenoids in the photosynthetic units is to prevent photo- 

 oxidative damage by chlorophyll. I do not intend to discuss this further 

 now, but no doubt various aspects of this work will be considered during 

 today's session. 



I wish to devote the remainder of my time to considering how caro- 

 tenoids are synthesized. Carotenoids are one class of a wide group of 

 natural products known as terpenoids ; these have a common characteristic 

 in that they are built up from isoprenoid (branched 5-C units). It is clear 

 from the work of Lynen, Popjak, and Bloch and their collaborators that 

 the 5-C unit from which steroids and other triterpenes are formed is 

 isopentenyl pyrophosphate (see Goodwin [2, 3] for details). The mech- 

 anisms involved in the formation of isopentenyl pyrophosphate from 



