Structural aspects of the milk clotting process. Comparative features with the blood clotting process.

The enzyme chymosin and its substrate, a casein fraction called k-casein, are involved in the milk clotting process. Recent data concerning the structure (peptide and sugar moieties) of various k-caseins and their role in casein micelles formation and stabilization are presented. The molecular events occurring during the primary phase of chymosin action on k-casein are discussed. Finally some structural features concerning more particularly the caseinoglycopeptides and the fibrinopeptides as well as the action of chymosin and thrombin involved in the milk and blood clotting processes are compared. Three examples of sequences of portions of k-caseins and fibrinogen presenting homology are presented.