232 Biological Chemistry. 



p. 242), and on the relatively large amounts of proline 

 and glutamic acid. 



(/) The Glutenins. Only two proteins of this class 

 have been described ; they are glutenin from wheat and 

 oryzenin from rice. They are insoluble in water, dilute 

 alcohol, and salt solutions, but soluble in dilute alkalis, 

 from which solution they can be precipitated by acids. 



(g) The Sclero-proteins. This group includes a miscel- 

 laneous class of substances, which are derived chiefly from 

 the supporting and connective tissues of animals (whence 

 the name). The chief examples of the group are hair, 

 horn, gelatin, and keratin. Certain of them, such as hair 

 and horn, are characterized by the large amount of cystine 

 which they yield on hydrolysis, and, therefore, also by the 

 relatively large amount of sulphur which they contain. 



II. The Conjugated Proteins. 



(a) The Nucleo-proteins. These proteins are widely 

 distributed in nature. They were originally discovered 

 in fish spermatozoa, which consist chiefly of nuclei, and 

 for this reason they have been supposed to form an im- 

 portant constituent of nuclei generally. They are also 

 found in the plant world, and the so-called tritico-nucleic 

 acid, from the wheat nucleo-protein, has been carefully 

 investigated. The nucleo-proteins contain the protein 

 group in some form of combination with nucleic acid. 



(6) The Glyco-proteins. This class, which includes 

 animal mucins and mucoid substances, has not been fully 

 investigated. The gly co-proteins are said to yield on 

 hydrolysis carbohydrate-like substances, amongst which 

 glucosamine, an amino-derivative of dextrose, has been 

 described. Cartilage is included amongst the glyco-pro- 

 teins, and yields on treatment with acids a peculiar sub- 

 stance known as chondroitin-sulphuric acid. 



