216 



PLANT BIOCHEMISTRY 



CHO 



(HC0H)3 



CH2OH 

 r)-ribose 



-ATP 



D-ribokinase 

 ^5-ADP 

 CHO 



(HioH)3 ghosphopentose 



CHO 

 HCOH 



HOCH c""'^-^'"""'""^^^ HOCH 



HCOH 



CH2OH 



D- xylose 



CHoOH 



D-xylulokinase 



CO 



jsomerase 



phosphoketopentose 

 -< >■ 



CH2OH 



CO 



D-xylulose 



I 

 HCOH 



1 

 CH2OH 



^— ATP 



^-^ADP 

 T 

 CH2OH 



CO 



phosphoketolase 



CH3COP 



acetyl- 

 phosphate 



H2COP 



l)-ribose-5P 



(HCOH), epimerase jjq^h 



+ TPP 



H2COP 



D-ribulose-oP 



A 



ADP-fr^ 

 ATP 



HCOH 



H2COP 



D-xylulose-5P 



A 



+ 



CHO 



I 

 HCOH 



I 

 H2COP 



3-phospho-IJ- 

 glyceraldehyde 



ADP 



ATP 



CHO 



I 

 HCOH 



i 

 (HOCH)^ 



CHoOH 



L-arabinose 



l.-arabino- 



isomerase 



CH9OH 



I " 



CO 



• I 



(HOCH), 

 CH2OH 



L-ribulosu 



L-ribulose-4- 

 epimerase 



CH2OH 



CO 

 (HOCH), 

 Ho COP 



I.-ribulose-5P 



FIGURE 9-4. The iiitciconvcrsions of certain pentoses as represented in 1959. The 

 isomcrization of D-arabinose to D-ribulose and the subsequent phosphorylation have 

 not been studied extensively in plants, and the names of the enzymes probably in- 

 volved have been omitted to indicate this deficiency. TPP signifies the cofactor 

 thiamine pyrophos|)hatc known 10 participate in other cleavage reactions of this 

 t)pc. 



