Figure 7.

α_S1-casein is present in a membrane-associated form in rough ER microsomes from goat mammary gland tissue. Aliquots of the microsomes prepared from goat mammary gland tissue were diluted and incubated in conservative (C) buffer in the absence of saponin (-), in conservative or non-conservative (NC) buffers in the presence of saponin (+), or were treated with carbonate buffer at pH 11 in the presence of saponin (pH 11). After centrifugation, supernatants (S) and pellets (P) were analyzed by SDS-PAGE followed by immunoblotting with an antibody against goat α_S1-casein. Immature α_S1-casein was quantified by densitometry and the proportion of the immature form in the supernatants and the pellets were expressed as percent of the total quantity of the casein (supernatant + pellet). The means of the results obtained from two animals are shown; bars indicate the variation of the single values from the mean. Relative molecular masses (kDa) are indicated. im. α_S1-cas: immature α_S1-casein.