Vegetable globulins are found in the cereals, leguminous plants, papaws and other vegetables, and are divided into two groups, myosins and paraglobulins. The vegetable myosins coagulate at from 55° to 60° and are precipitated from a saline solution by removing the salt by dialysis. In this form, however, they lose their true nature as globulins, becoming insoluble in weak saline solutions.
The vegetable paraglobulins are coagulated at from 70° to 75°. Vegetable vitellin, which is not included in this classification, can be obtained in a crystalline form and of remarkable purity.[339]
Albuminates.—This name is given to the compounds of the proteids with metallic oxids or bases, and also to acid and alkali albumins. They are insoluble in water or dilute neutral salts, but easily soluble in strong acids or alkalies. Casein is a type of this group.
Acid albumin is made from egg albumin by treatment with hydrochloric acid; alkali albumin is formed in egg albumin by the action of a dilute alkali; trinitroalbumin is formed from dry albumin by treatment with nitric acid; casein or caseinogen is the chief proteid in milk.
The chief vegetable albuminates are legumin and conglutin. Legumin is a vegetable casein and occurs chiefly in peas, beans and other leguminous seeds. It is prepared by extracting the meal of the seeds mentioned with dilute alkali, filtering the extract, precipitating with acetic acid, washing the precipitate with alcohol, and drying over sulfuric acid. Treated with sulfuric acid it yields leucin, tyrosin and glutamic and aspartic acids. Conglutin is prepared in a similar manner from almonds.
It is probable that these bodies do not exist as such in the fresh seeds in question but are produced therein from the other proteids by the alkali used in extraction. A further description of vegetable proteids will be found in the special paragraphs devoted to the study of these bodies in the principal cereals.
Proteoses.—This name is applied to proteids which are not coagulated by heat, but most of them are precipitated by saturated solutions of neutral salts. They are also precipitated by nitric acid. They are formed from other proteids by the action of proteolytic ferments. The albumoses represent this group.
Protoalbumose is soluble in distilled water and weak saline solutions and is precipitated by mercuric chlorid and copper sulfate.
Heteroalbumose is insoluble in distilled water, but soluble in weak saline solutions, from which it separates when the salts are removed by dialysis. Deuteroalbumose is soluble in distilled water and saline solutions and is not precipitated on saturation with sodium chlorid. It is thrown out by mercuric chlorid but not by copper sulfate.
Vegetable proteoses are known as phytalbumoses, two of which have been found in the juice of the papaw mentioned above. They have also been found in cereals.