Unlike other organic substances, protein contains nitrogen. The average content of nitrogen in protein - 16 %.
Depending on the composition of all proteins are divided into two groups: simple and complex. Simple proteins include albumins, globulins, which are found in plants and animals, glutelin, that prolamins - only in plants, histones and protamines - only in animal tissues. Complex proteins consist of amino acids and non-protein parts: lipoproteins - compounds of proteins with lipids, nucleoproteins - nucleic acids, phosphoprotein - with the remnants of phosphoric acid, glycoprotein - with carbohydrates, chromoproteids - with colorants, metalloprotein - metals (Fe, si, Mg, Zn, etc.).
In feed grains is dominated by simple proteins, in the green grass - complicated. Nucleoproteins are contained in the nuclei of plant and animal cells. Phosphoprotein, chromoproteids, lipoproteids glycoprotein and are found in vegetable and animal organisms. Phosphoprotein belongs to the casein of milk, for chromoproteids - hemoglobin.