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.
103/454 page 87
![readily soluble in water, but less so in alcohol. It hydrolyses to a mixture of glucose and fructose in equal quantities. Heated to 160° it yields a glass-like substance—barley sugar—and at 200° the brown mixture we call caramel. Sucrose does not reduce alkaline copper solutions, nor does it form an osazone, so that it is neither actually nor potentially an aldehyde nor a ketone. Sucrose is dextro-rotatory, [a]2£° — -f 66-5°. When its solution is hydrolysed the rotation of the mixed hexoses is laevo-rotatory, so that an inversion of the rotation has taken place, and we speak of the process as the inversion of cane-sugar. The explanation lies in the fact that the specific rotation of fructose is much more strongly to the left ([a]D = — 92*0°) than that of glucose is to the right ([a]D — -f- 52-5°), so that, as an equal mixture of the two is produced, the net result as observed is a rotation to the left. A specific enzyme sucrase, found in yeasts, moulds, and some of the higher plants, and in the intestinal juice of mammals, is sometimes named, on this account, invertase. Sucrose, treated with acetyl chloride, yields an octo-acetate, indicating that the sugar has eight free hydroxyl groups. Its constitutional formula is given on p. 89. Numerous attempts have been made to synthetise it, apparently without success. Lactose, or milk-sugar, occurs in the milk of all mammals, and is the only sugar and the only carbohydrate in the diet of sucklings. It is not found in plants. Cow’s milk contains 4 per cent, of it, human milk 5 to 7 per cent. When the whey of milk is concentrated, lactose, which is not very soluble, crystallises out in hard and gritty crystals. It is, as we know from experience, not very sweet, and if milk contained an equal quantity of sucrose it would prove a nauseating food. Lactose reduces alkaline copper solutions, and gives a specific osazone, suggesting that it contains a free, or, at any rate, a potential, aldehyde group. It is not fermented by pure yeast. It hydrolyses to a mixture of equal quantities of glucose and galactose. It is dextro-rotatory, its specific rotation being nearly the same as that of glucose. Maltose, or malt-sugar, according to recent researches, is present in distinct amounts in the tubers of certain climbing plants. It is produced by the hydrolysis of starch or glycogen by the enzyme amylase. (If acid is used for the hydrolysis the maltose cannot be separated but is immediately hydrolysed further to glucose.) Maltose is hydrolysed by the specific enzyme maltase (present in intestinal juice) to two molecules of glucose.](https://iiif.wellcomecollection.org/image/b2992859x_0103.jp2/full/800%2C/0/default.jpg)
