98 NITROGEN METABOLISM 



acid, though usually only if much larger amounts are sup- 

 plied. When small inocula are used, the glutamine require- 

 ments of Strep, haemolyticus (groups A and C) are absolute 

 and cannot be replaced in this manner [10]. Streptococci 

 decompose glutamine to glutamic acid and ammonia only 

 when they are fermenting glucose, and the presence of small 

 amounts of glutamine was observed to stimulate the fer- 

 mentation of glucose by washed cell suspensions of all the 

 streptococci examined, irrespective of their glutamine re- 

 quirements during growth [27]. This stimulation was far 

 greater than that produced by an equivalent amount of 

 ammonium glutamate, and the more dilute the suspension, 

 the greater the stimulation. Glutamine here appears to func- 

 tion by restoring the intracellular concentration of a dif- 

 fusible co-factor to an optimal value. Similar results were 

 later obtained with Ln. mesenteroides, Lb. arabinosus [45] and 

 CI. tetani [24]. Unlike the streptococci, Pr. morganii [26], 

 Esch. colt, and CI. welchii [18] are able to hydrolyse the amide 

 group of glutamine in the absence of glucose fermentation. 

 Asparaginase — the enzyme system catalysing the hydrolysis 

 of the amide group of asparagine — is widely distributed in 

 fungi, yeasts and bacteria [cf. 50], and for this reason aspara- 

 gine is frequently incorporated in media as a convenient 

 source of readily available carbon and nitrogen. Asparaginase 

 has been found, for example, in autolysates of P^. pyocyanea, 

 Esch. colt, B. siibtiUs and Pr. vulgaris. Asparagine is an 

 essential nutrilite for some strains of Ln. mesenteroides and 

 Strep, lactis. 



Glutamic acid is also a constituent of the folic acid factors, 

 substances essential for the growth of Strep, faecalis R and 

 Lb. casei and of key importance in the metabolism of all 

 organisms. These factors contain a pterin linked to ^-amino- 

 benzoic acid (PAB) which is in turn coupled through the 

 amino group to one or more residues of glutamic acid (one 

 in synthetic folic acid, three in the fermentation Lb. casei 

 factor and seven in vitamin B^ conjugate). The linkages be- 

 tween PAB and glutamic acid and between the various glut- 

 amic acid molecules probably involve the y-carboxyl groups 

 of the amino-acid. Whilst the enzyme systems in which folic 



