THE PROTEINS (05 



protein and carbohydrate radical, on prolonged boiling with dilute mineral 

 acids or by the action of alkalies. They may be divided into the two main 

 groups of mucins and mucoids. 



The mucins play a large part in the animal kingdom as protective agents. 

 They form the slimy secretion which covers the inner surface of the mucous 

 membranes and the outer surface of many marine animals, and is secreted 

 either by the goblet cells of the epithelium or by special groups of cells 

 collected together to form a mucous gland. They may be precipitated from 

 their solutions or semi-solutions by the addition of acids, and after precipita- 

 tion need the addition of alkalies for their re-soluti6n. They are not coagu- 

 lable by heat. The presence of their protein moiety causes them to give 

 the various typical protein tests, such as the xanthoproteic, Millon's, the 

 biuret reaction, and so on. Prolonged boiling with acids splits the molecule, 

 with the production of acid metaprotein and albumoses and glucosamine. 

 From the mucin of frogs' eggs a similar treatment results in the production of 

 galactosamine. 



With the mucins may be classified certain bodies which have been derived from 

 ovarian cysts, namely, pseudomucin and paramucin. Pseudomucin occurs as a con- 

 stituent of the colloid material from ovarian tumours. It forms slimy solutions which 

 do not coagulate by heat and are not precipitated by acetic acid. It is precipitated 

 by alcohol, the precipitate being soluble in water even after standing a long time under 

 the alcohol. On boiling with acid it gives a reducing substance. Paramucin differs 

 from the above in reducing Fehling's solution before boiling with acids. Otherwise 

 it resembles pseudomucin. Leathes, in investigating this txTdy, isolated from it & 

 reducing substance which apparently was an ammo-derivative of a disaccharid**. 

 perhaps in combination with glycuronic acid. 



The mucoids include a number of substances which may be extracted 

 from various tissues by the action of weak alkalies, e.g. from tendons, bone, 

 and cartilage. The best studied example of this group is the chondromucoid 

 which, with collagen, forms the ground substance of cartilage. Chondro- 

 mucoid is especially rich in sulphur and gives protein by long treatment with 

 weak alkali. On boiling for a short time with acid it is decomposed into 

 sulphuric acid and chondroitin, and this latter, on further action of the acid, 

 is converted into a substance chondrosin, which is certainly an amino- 

 derivative of a polysaccharide containing the elements of glycuronic acid and 

 an amino-disaccharide. Chondroitin-sulphuric acid occurs not only in 

 cartilage but also in bone, yellow elastic tissue, white fibrous tissue, and 

 constant constituent of the lardacein or amyloid substance which occurs as f 

 deposit in the middle coat of the blood-vessels as the result of syphi 

 long-continued suppuration, and gives rise to the condition known a 

 daceous disease.' Another example of this class of mucoi'ds is ovoi 

 which is a constituent of egg-white. In order to prepare ovomucoid tl 

 globulin and albumin are precipitated by boiling diluted egg-white 

 the nitrate ovomucoid can then be thrown down by alcohol, 

 has been prepared from blood serum. Both these mucoids yie 

 amount of reducing substance on hydrolysis. Thus from 10 

 mucoid it is possible to prepare 30 grm. of glucosamine. ^ 



