THE CARBOHYDRATES ^ 



Glucosamine, C 6 H 13 N0 5 , has the structural formula : 



CH 2 OH 

 (CH.OH) 3 

 GH.NH 2 



CHO 



It is obtained from chitin, which forms the exoskeleton of large numbers 

 of the invertebrate, by boiling this with concentrated hydrochloric acid It 

 is stated to have been obtained as a decomposition product of certain proteins 

 and their derivatives, such as the mucins. It is of special interest as affording 

 an intermediate product between the carbohydrates and the oxy-amino 

 acids which can be obtained by the disintegration of proteins. In solution 

 it is dextro-rotatory, reduces Fehling's solution, and gives an osazone 

 resembling that derived from glucose. 



GLYCURONIC ACID, C 6 H 10 7 , may be regarded as one of the first results 

 of oxidation of the glucose molecule. The group which has undergone 

 oxidation is not the readily oxidisable CHO group, but the CH 2 OH group at 

 the other end of the molecule. The formula of this acid is therefore : 



COOH 

 (CH.OH) 4 



CHO. 



In the free state it does not occur in the animal body. It is constantly found 

 in the urine after administration of certain drugs such as phenol, camphor, or 

 chloral, and then occurs as a conjugated acid with these substances. These 

 conjugated acids are laevo-rotatory, though the free acid is dextro-rotatory. 

 In the free state it reduces Fehling's solution and gives an osazone which is not 

 sufficiently characteristic to distinguish from glucosazone. It does not 

 undergo fermentation with yeast. This test is therefore the best means of 

 distinguishing the acid in urine from glucose. 



THE FORMATION OF GLUCOSIDES 



The graphic formulas given on p. 61 do not explain all the possible modes of arrange- 

 ment of the groups of the sugar molecules. Many of these sugars, when dis 

 water, present the phenomenon known as multi -rotation. If their rotatory power 

 be taken immediately after solution, it is found to be greater or less than the r 

 power taken some hours or days later. Glucose, for instance, immediately a 

 tion, has a high specific rotatory power, which diminishes rapidly ii 

 boiled, and more slowly if it be allowed to stand. Finally, the specifi 

 becomes constant at 4- 52-5 D. This change in rotatory power seems to b 

 with a change in the arrangement of the groups, the aldose, for-ex; 

 by the shifting of a mobile oxygen atom, what is known as a lacl< 



