Many researchers have demonstrated that the G–L dipeptide could be metabolized in rats, and that lysine was incorporated into rat tissue41, 42 and 43. However, the bioavailability of the G–L moiety in the crosslinked proteins has not yet been demonstrated. This may be because of the impracticality of using guinea pig liver TGase for large-scale preparation of crosslinked proteins for animal feeding studies. Fortunately, with abundantly available MTGase, crosslinked caseins have been prepared in kilogram-scale quantities, and were fed to rats to evaluate the nutritive value of lysine in the G–L moiety. Rats fed the crosslinked caseins grew normally, compared with rats fed native caseins[44]. It is therefore suggested that the G–L moiety in the crosslinked caseins is cleaved and the lysine is utilized in the body.