Define Casein - Tests for Presence of Exoenzymatic Activity?

Casein is a major milk protein composed of various amino acids linked through peptide bonds. Extra-cellular enzyme protease degrades proteins to produce peptones, polypeptides, dipeptides and finally to amino acids (proteolysis). Amino acids are transported to the cell and used for synthesis of structural and functional cellular proteins. Release of proteases by microorganisms can be detected by use of milk agar (nutrient agar supplemented with milk). The medium is opaque. Following inoculation and incubation, loss of opacity around the growing organism indicate positive result, i.e., synthesis of proteases.