abundance ^C and ^H ratios. Genetic transformation of 

 Chlamydomonas (Boynton et al., 1990) is being used to evaluate the 

 molecular bases for changes in isotopic fractionation (Osmond et 

 al., 1991). 



Energetics of Global Carbon Cycling 



Two geochemical indicators of the biospheric role in the 

 global carbon cycle are the following: 



a. The annual variation in the northern hemisphere of 1J C/ lf -C 

 in atmospheric C0 ? , consistent with participation of Rubisco in the 

 draw down of COo; and 



b. The annual variation in the northern hemisphere of 18 o/ 16 

 in atmospheric C0 2 , consistent with exposure of the entire 

 atmospheric C0 ? pool to carbonic anhydrase in leaf water, which can 

 be a much larger effect than that due to cloud-water equilibration 

 or ocean mixing. 



Tans showed that in 1979 the northern hemispheric terrestrial 

 biosphere was the largest contributor to net flux of COp via (a) , 

 but in 1989 the southern ocean biosphere was the dominant path for 

 the net flux (Tans et al., 1990). Yakir showed, for example, that 

 the delta 0-18 of metabolic water, and not transpiring water, was 

 probably the source of (b) . Further research in both areas could 

 underpin fundamental issues in the global carbon cycle. This 

 research can be facilitated by the following molecular techniques 

 (Yakir et al. , 1991) . 



(1) Specificity factor of Rubisco. 



Rubisco, the primary carbon assimilating enzyme, is found in 

 several of forms which are diagnostic for groups of organisms. The 

 most common hexadecameric (L Q Sg) form has evolved to perform 

 carboxylation/ oxygenation at different rates and efficiencies. 

 While the amount of mRNA for LSU and SSU subunits probably has no 

 indicative value, it is possible that peptide antibodies against 

 specific functional domains or protein modules can be designed. 

 However, the lack of knowledge, especially about chrysophyte, 

 rhodo-, phaeo-, Rubisco enzymes, prohibits such generalizations. 

 In addition, even among cyanobacteria and photosynthetic bacteria, 



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