Primary Protein Derivatives: Derivatives of the protein molecule apparently formed through hydrolytic changes which involve only slight alterations.
Proteins: Insoluble products which apparently result from the incipient action of very dilute acids or enzymes. Ex : Casein (curdled milk), fibrin (coagulated fibrinogen).
Metaproteins: Products resulting from the action of acids and alkalis whereby the molecule is sufficiently altered to form proteins soluble in weak acids and alkalis, but insoluble in neutral solvents.
Coagulated proteins: Insoluble proteins which result from 1. the action of heat on protein solutions or 2. The action of alcohol on the proteins. Ex : Cooked egg albumin, or egg albumin precipitated by alcohol.
Secondary Protein Derivatives: Products of further hydrolytic cleavage of the protein molecule.
Proteases: Soluble in water, not coagulable by heat. Precipitated by saturating their solutions with ammonium sulphate.
Peptones: Soluble in water not coagulable by heat and not precipitated by saturating their solutions with ammonium sulphate. These represent a further stage of cleavage than the proteoses (the term ‘peptone’ is generally used to all protein digestion products not coagulated by boiling and containing a mixture of proteases, peptones and peptides).
Peptides: These are compounds containing two or more amino acids. Anhydride of two amino acids is called a dipeptide, one having three amino acids a tri – peptide and one containing several amino acids, a polypeptide. Peptides result from the further hydrolytic cleavage of the peptones.