Microheterogeneity of the caseins

Each of the four caseins, a i, tx 2 P k, exhibits variability, which we will refer to as microheterogeneity, arising from five causes  

Variability in the degree of phosphorylation. Each of the four caseins is phosphorylated to a characteristic but variable level  

Disulphide bonding. The two principal caseins, and contain no cysteine or cystine but the two minor caseins, a. 2 contains two 

Isolated S s2-casein in solution is also very susceptible to plasmin eight peptide bonds are hydrolysed with the production of 14 peptides. Plasmin also hydrolyses as2-casein in milk but the peptides formed have not been identified, although at least some are included in the proteose-peptone fraction. 

Although less susceptible than and as2-caseins, isolated a i-casein in solution is also readily hydrolysed by plasmin. It has been suggested that a minor ill-defined fraction of casein, called A-casein, consists of plasmin-produced fragments of -casein, but the situation is unclear. 

---

Fournet, B., Fiat, A.-M., Montreuil, J. and Jolles, P. 1975. The sugar part of K-casein from cow milk and colostrum and its microheterogeneity. Biochimie 57, 161-165. 

---