270 



GERTRUDE E. GLOCK 



HC=0 



I 

 HCOH 



I 

 HOCH 



I 

 HCOH 



I 

 CH2OH 



H2COH 



c=o 



I 



CHOH 



I 

 CHOH 



H2COH 



I 

 HC=0 



■hc=o 



I 

 CHOH 



* 

 CH3 



COOH 



+ 



COOH 



I 

 CHOH 



CH3 



CH2OPO3H2J L CH20P03H2_ 



Fig. 9. Suggestive method of degradation of D-xylose-1-C'^ by Lactobacillus pen- 

 tosus (after Gest and Lampeni*'^). 



lus pentoaceticus using L-arabinose-1-C"."" In both cases, all the C* was found in 

 the methyl group of the acetic acid. This observation that the aldehyde carbon is 

 the source of the methyl carbon of the acetate suggested the intermediary formation 

 of a ketopentose which was believed to be phosphorylatfed as shown in Fig. 9. When 

 L. pentosus was grown on D-xylose or L-arabinose, cells were obtained which fer- 

 mented D-ribose in addition to these two pentoses.'^" In addition, extracts of these 

 cells degraded ribose-5-phosphate rapidly and catalyzed the phosphorylation of 

 pentoses by ATP.'"'' It was suggested that D-xylose and L-arabinose are converted 

 to an ester with the ribose configuration prior to cleavage. This was supported by the 

 formation of ribose-5-phosphate in good yield when D-xylose and ATP were incubated 

 with bacterial extracts, the isolated pentose phosphate fraction containing approxi- 

 mately 80% ribose-5-phosphate with small amounts of ketopentose phosphate and 

 possibly some heptulose phosphate. The mechanism of conversion of xylose to ribose- 

 5-phosphate is obscure. It is possible that a xylose phosphate is the initial product, 

 but xylose-5-phosphate is inert in this system and cannot therefore be an intermedi- 

 ate. It has recently been shown" that when D-xylose is incubated with bacterial ex- 

 tracts in the absence of ATP, it is converted into D-xylulose (see Sect. VI.3). This 

 suggests that fermentation of D-xylose possibly involves formation of D-xylulose and 

 subsequent phosphorylation with ATP. Epimerization of the hydroxyl group on C3 

 of the hypothetical xylulose phosphate would be necessary to obtain ribose-5-phos- 

 phate. These adaptive bacterial enzymes as well as those described by other workers 

 are included in Fig. 7. Adaptive bacterial pentokinases, which catalyze the phospho- 

 rylation of pentoses by ATP, have been reported for D-ribose,"^ -"^ D-arabinose,'" 

 L-arabinose, "2 D-ribulose,'"* and D-xylose" •"^•"' and suggested, by indirect evidence, 

 for D-xylulose." It is possible that phosphorylation of D-arabinose might consist of 

 initial isomerization to D-ribulose" and subsequent phosphorylation of this to ribu- 

 lose-5-phosphate. A specific ribokinase has also been demonstrated in yeast and the 

 end-product identified as ribose-5-phosphate."'' 



1"^ D. A. Rappoport, H. A. Barker and W. Z. Hassid, Arch. Biochem. and Biophys. 



31, 326 (1951). 

 "» J. O. Lampen and H. R. Peterjohn, J. Bacieriol. 62, 281 (1951). 

 "' S. S. Cohen, D. B. M. Scott, and M. C. Lanning, Federation Proc. 10, 173 (1951). 

 "^ J. de Ley, Bull. Assoc, dipldmes microhiol. Fac. pharin. Nancy p. 1 (1952). 

 ^" R. M. Hochster and R. W. Watson Ahstr. 2nd. Intern. Congr. Biochem., Paris 



p. 291 (1952); Nature 170, 357 (1952). 

 "* H. Z. Sable, Biochem. el Biophys. Acta 8, 687 (1952). 



