DEGRADATION OF MYOSIN BY ENZYMES OF THE DIGESTIVE-SYSTEM - COMPARISONBETWEEN NATIVE AND OXIDATIVELY CROSS-LINKED PROTEIN

We compared proteolysis of H2O2/hemin-cross-linked myosin and the nati ve protein. Pepsin, trypsin, and chymotrypsin, representative enzymes of the mammalian digestive tract, and the plant enzyme papain were cho sen as proteases. Under conditions which caused prominent degradation of the native myosin, only minimal degradation of the cross-linked pro tein was observed when individual enzymes were applied. Successive pro teolysis by pepsin at gastric pH (1.85) followed by trypsin and chymot rypsin at duodenal pH (8.9) also showed retarded proteolysis of cross- linked myosin. At low pH both myosin forms precipitated, but by elevat ion of the pH only cross-linked myosin was partially resolubilized and the solubility was augmented following its minimal proteolytic degrad ation. It was concluded that although in general oxidatively modified proteins are susceptible to proteolysis, oxidatively cross-linked myos in is resistant. The data suggest that decreased digestibility of cros s-linked myosin may lead to reduced quality of oxidized muscle foods.