320 SHLOMO HESTRIN 



of cells in a glucose solution), the yield of fibre, as judged on the basis of 

 fibril incidence in an electron-microscope field, was significantly increased. 

 However, in view of the complexity of design and the sparsity of quantita- 

 tive information in these experiments, the chemical interpretation of these 

 results remains still uncertain. 



In a recent note, Klungsoyr [9] revealed the existence in A. xylimim of 

 a disproportionating enzyme system which can catalyze a transfer of glu- 

 cosyl units from soluble cellodextrins into an insoluble cellulose fraction. 

 This may indeed prove an important clue towards the understanding of 

 the intermediary mechanism in cellulose synthesis. 



Although hexose phosphate (a- and ^-glucose- 1 -phosphate andUDPG) 

 supplied to the cell exogenously does not yield cellulose, the assumption 

 that hexose phosphate is an intermediary of cellulose production can be 

 strongly supported. In this connection it may be noted that these cells 

 readily form cellulose both from hexonic acids (gluconate, 2-ketogluconate, 



TABLE I 



Distribution of Radioactivity in Cellulose 

 Formed from Specifically- Labelled Fructose 



Substrate 



Total radioactivity in 



cellulose monomer 



("o of that in 



fructose) 



Distribution of radioactivity in 



cellulose monomer (total in 



monomer = 100) 



Ci 



C2 C3 C4 Cs 



C6 



[ I -i*C] -fructose 

 [2-^*C]-fructose 

 [6-"C]-fructose 



37 to 42 



76 



103 



17 

 6 



63 

 o 



1 1 

 o 



5-ketogluconate) and from other compounds (glucose, fructose) which 

 could readily be converted by an Acetobacter cell into hexose phosphate. 

 Furthermore, the view that hexose phosphate is an intermediate is also 

 supported by the observation that radioactivity recovered in cellulose 

 formed from specifically-labelled glucoses presents a distribution pattern 

 quite diff^erent from that in the original substance but which is similar 

 in unique features to the pattern which would arise if the intermediate 

 on the pathway between exogenous hexose and formed cellulose is hexose 

 phosphate in pentose cycle [10]. An analysis of radioactive carbon distri- 

 bution in the cellulose afforded from specifically-labelled fructose was 

 carried out in our laboratory by Dr. Gromet-Elhanan with results 

 shown in Table I. These findings have given additional support to the 

 view that the cellulose arises from hexose phosphate in a pentose cycle. It 



