CARBON METABOLISM 257 



iiiterveiition of a pliosphate-donur complex with a high 

 energy content, in such a way that an aliphatic compound, 

 probably an aldehyde, is carboxylated and reduced with 

 the ultimate formation of carbohydrates. The general 

 reaction is : — 



Phosphate-donor -f RH ?==^ free donor + RH-phosphate 



CO 2 

 RH-phosphate ^ R.COOH + inorganic phosphate 



carboxylase 



When RH is an aldehyde and if the phosphate donor is 

 considered to be adenosine triphosphate (which is very 

 probable, see p. 275) the reactions are : — 







i! !! II 



C10N5H12O3— 0— P— 0— P— 0— P— OH + R.CHO + HoO 



III 

 OH OH OH 



(Adenosine triphosphate) ^1 



Enzyme 







II il ^ II 



C10X5H12O3— 0— P— 0— P— OH + R.C 0— P— OH + 2H 



1 I I 

 OH OH OH 



(Adenosine diphosphate) 







^ il Enzyme || 1| 



R.r;_0— P— OH + CO2 + 2H ^=^ R_(j_c— OH + H3PO4 



ci„ 



o 



II II Enzyme 



R— C— C— OH + 2H ^=^ R.CHOH.COOH 



Enzyme 

 R.CHOH.COOH -f phosphate -donor ^=^ R.CHOH.CO.PO3H2 + donor 



Enzyme 

 R.CHOH.CO.PO3H2 + 2H F-"=^ R.CHOH.CHO + H3PO4 



The aldehyde R.CHOH.CHO, which can be regarded 

 as a carbohydrate, could give rise to polysaccharides 



