PENTOSES AM) II EX OSES 657 



bacterial ilccoiiiiKJsitiou of other carhohyiliatcs, it is inevitable that alimentary 

 pentoaurias should oecasionaily occur in nearly every normal individual, and, a.s a 

 matter of fact, most normal urines give reactions which indicate the ])resence of 

 some pentose (Cremer, Funaro, Cominotti). Vice versa, one may ccMiclude that 

 very little jjcntose normally occurs in the blood, since otherwise more of it would 

 appear in the normal urine than does; and finally, that pentoses must play but a 

 minor role in the general metabolism of the carbohydrates. Therefore it is highly 

 imi)robable that during the breakdown or synthesis of glucose in the body the hex- 

 oses split to any extent into a pentose and fornuUdehyde. The .same holds good 

 for the behavior of hexoses in the presence of alkali. They split almost exclu- 

 sively into chains of 2, 3 and 4 carbon atoms (Xefj. 



Chronic Pentosuria-* 

 The literature contains reports of some 30 cases in which consid- 

 erable quantities of pentose have been excreted steadily in the urine 

 regardless of the character or quantity of the food. Even during a 

 fast the quantity excreted has remained virtually constant in some 

 cases. Outputs as high as 36 grams per day have been recorded. 

 Such quantities of pentose could not be introduced into the body from 

 without by any known means without causing pentosuria of marked 

 degree. Accordingly, in some cases there is cither an overproduction 

 of endogenous pentose, or an abnormal entry into the blood stream 

 of pentose which is normally bound in the tissues. The process would 

 then be analogous to that in which lactose from the mammary glands 

 occasionally gains access to the general circulation and appears in the 

 urine. This conclusion is confirmed by the work of Bial, Blumenthal 

 and Tintemann, who found that certain pentosurics displayed no les- 

 sened tolerance for administered pentose. The origin of the pentose 

 is unknown. Nucleo-protein of cell nuclei, and galactose have been 

 suggested as possible sources. The disease has been found in differ- 

 ent members of the same family and appears to be a harmless anomaly. 

 The pentose found in the urine in cases of all types has sometimes 

 been reported as optically inactive, sometimes as dextro- or levo- 

 rotatory; 1-arabinose (dextro-rotatory), d-xjdose and d-xyloketose 

 appear to have been identified.-^ 



HEXOSES 

 Chemical Introduction. — Structural theory demands the existence of 32 

 isomeric hexo&e sugars of the formula CeHijOg. The behavior of the hexoses 

 when dissolved in very dilute alkali makes it convenient to consider them in four 

 natural series of eight members each. Thus one series comprises the 8 hexoses 

 whose structural formulae appear below. This may be called the d-glucose series. 



(1) (2) (3) ■ (4) (5) (6) (7) (8) 



CHO CHO CHoOH CHO CHO CH5OH CH-OH CH-OH 



H-(4-0H HO-i-H 60 H-i-OH HO-t-H 60 H-COH HO-C-H 



HO-(i-H H0-(i-H HO-c'^-H K-6-0K H-6-OH H-t-OH CO tO 



H-(i-OH H-(i-OH H-(!^OH H-(LoH H-C-OH H-C-OH H-(!:-OH H-i-OH 



H-i-OH H-i-OH H-ioH H-i-OH H-C-OH H-C-OH H-C-OH H-C-OH 



CH2OH CH2OH CH20H CH2OH CHiOH CHiOH CH3OH CHjOH 



d-pseudo 

 d-glucose d-mannose d-fructose d-allose d-latose fructose a-d-glutose ^-d-glutose 



2<See Garrod. ''Inborn Errors of Metabolism," Oxford Med. Publ., 1909; 

 Lancet, July, 1909. 



25 For literature see ffiUer, Jour. Biol. Chem., 1917 (30). 129. 



42 



