These are divided into primary and secondary protein derivatives. Primary protein derivatives are those that have been slightly modified by the incipient action of water, very dilute acids, or enzyms, or are the result of the action of acids and alkalies whereby products soluble in weak acids and alkalies are formed. Coagulated proteins resulting from the action of heat and alcohol are classed in this division.

Secondary protein derivatives are those in which the modifying changes (hydrolytic or the taking up of water), through the action of acids or enzyms, have proceeded beyond the incipient stage with the formation of bodies that are soluble in water. In this division, the most important compounds are the proteoses and the peptones, the latter having suffered a greater change by hydrolysis than the former.

Primary Protein Derivatives

58. Proteans And Metaproteins

When proteins are acted upon by acids or alkalies, they are modified in proportion to the strength of the reacting acid or alkali and the length of time that the action continues. With acid or alkalies of sufficient strength, there are formed products soluble in weak acids and alkalies.

69. Coagulated Proteins

There are several agents which convert albumins and other proteins into a coagulated mass, such as a boiling heat, alcohol, and certain neutral salts and the action of an enzym. For instance, with albumin from flesh or the white of an egg, boiling water converts it into a coagulum that is insoluble in water and is only rendered soluble by such agents as acids and alkalies upon heating.

Dropping a soluble protein into alcohol has the same effect. Globulins are, as a rule, affected in the same way. The nature of this modification is not known.