A textbook of biochemistry for students of medicine and science / by A.T. Cameron.
- Alexander Thomas Cameron
- Date:
- 1938
Licence: In copyright
Credit: A textbook of biochemistry for students of medicine and science / by A.T. Cameron. Source: Wellcome Collection.
95/454 page 79
![solution at least two different optically active substances, which are gradually changing, one into the other. And it has been proved that two different forms of d-glucose do exist, isomers, but differing in rotatory power. One, a-d-giucose, crystallises at ordinary temperatures from 70 per cent, ethyl alcohol, and has a molecular rotation of [a]D = + 110°. The other, p-d-glucose, crystallises from aqueous solutions at temperatures above 98°, and for it [a]D = + 19°. If glucose contained only four asymmetric carbon atoms, then the existence of these two forms would be impossible, since with four asymmetric atoms there are only possible sixteen different arrangements, and the sugars corresponding to these are all known. Evidently, therefore, d-glucose in solution has in reality five asymmetric carbon atoms. This has been proved. Two methyl-d-glucoses (simple glucosides) have been prepared, which are believed to be : (i) II—C—O—CH, CH2OH a-Methyl-d-glucoside (2) CH,_0—C—II CHaOH fi-Methyl-d-glucoside Each of these is hydrolysed by an appropriate enzyme. The first, the a-compound, yields a glucose of high rotatory power. On adding a drop of ammonia the rotation rapidly falls to the equilibrium value of ordinary glucose. When the second is hydrolysed, glucose of low rotatory power is produced, and when ammonia is added the rotation rapidly increases. Hence we may consider that the formulae of these two d-glucoses are : 0) H—C—OH H—C—OH I HO—C—H H—A—OH hJ— o d:H. OH a-d-Glucose (»•) HO—C—H CH2OH fi-d-Glucose](https://iiif.wellcomecollection.org/image/b2992859x_0095.jp2/full/800%2C/0/default.jpg)
