1686 CHEMICAL PATH OF CARBON DIOXIDE REDUCTION CHAP. 36 



Similar experiments had been described earlier by Benson (1950). According to 

 him, higher plants (barley) and purple bacteria (Rhodospirillum) contain a phosphatase 

 which has considerable resistance to heat. Immediate killing of leaves with boiling 

 alcohol produces no free hexoses or trioses and very little free glyceric acid ; but freezing 

 in liquid air, grinding and extraction with boiling ethanol gives considerable amounts of 

 free sugars and acids. 



Buchanan, Lynch, Benson, Bradley and Calvin (1953) called attention 

 to a previously unidentified spot on the paper chromatogram, which ap- 

 pears after about 30 sec. of steady photosynthesis in C*02, and is situated 

 in the same general area as the known sugar phosphates. This material 

 very easily produced glucose by hydrolysis. More extensive chromato- 

 graphic study revealed that it also contained galactose and mannose. It 

 was surmised that the spot may contain uridine diphosphates of these and 

 other hexoses (compounds described by Leloir). This surmise was con- 

 fi.rmed by co-chromatography with pure compounds and other chromato- 

 graphic tests. The hexoses contained in esters of this type constitute a 

 large fraction of labelled, nonpolymerized hexoses present after several 

 minutes of steady photosynthesis in C*02. Adenine phosphate, adenosine- 

 5 '-phosphate and uridine-5 '-phosphate also were found in the hydrolysate 

 from this radioactive spot. 



Benson, Kawaguchi, Hayes and Calvin (1952) gave fig. 36.21 for the 

 course of tagging of several sugar phosphates, showing that fructose is 

 labelled ahead of glucose (and mannose). Calvin and Massini (1952) 

 suggested that the synthesis of sucrose occurs by the interaction of fructose 

 phosphate with the above-described glucose phosphate-uridine complex 

 (uridine diphosphoglucose). The first product could be sucrose mono- 

 phosphate. By treating the material from the hexose monophosphate area 

 of the chromatogram by a phosphatase free of invertase, Buchanan (1954; 

 cf. Buchanan, Bassham et al. 1953) was able to demonstrate the actual 

 presence of sucrose monophosphate, lending considerable support to the 

 hypothesis. Calvin and Massini suggested that compounds of the type of 

 uridine diphosphoglucose may serve as "glucose donors" also in the sub- 

 sequent formation of polysaccharides, 



11. Effect of Poisons and pH. on CO2 Fixation 



It was mentioned in section 6 that malonate was found to inhibit the 

 tagging of malic acid, without much effect on the yield of sugar synthesis. 

 Following are observations on the effect of some other poisons, according to 

 Calvin et al. (1951) (based on the experiments of Stepka 1951). 



In the presence of 1.5 X 10~* M iodoacetamide, the total uptake of 

 C* was reduced by 90%, but the formation of labelled sucrose was not af- 

 fected at all. (At lower concentrations of the inhibitor, it was even in- 



