FIGURE 4.

Characterization of the E. histolytica N-glycans by in vivo labeling and glycosylhydrolase digestions. E. histolytica N-glycans, which were prepared as in Fig. 2, were treated with glycosylhydrolases, and digestion products were identified according to retention times (r.t.) of known standards (e.g. Man₃GlcNAc₂). For isomers H6.2, H6.5, and H7.1, the dashed line enclosing the Manα1,6-arm indicates what corresponds to the residual fragment 11.5, which was fully characterized in a separate [U-¹⁴C]Glc-labeling experiment. Note that jack bean α-mannosidase (JBAM) removes an exposed Manα1,3- (as in isomer H4.3), but it does not remove the Manα1,6-unless the Manα1,3-arm is digested first. Hence, isomer H4.2 becomes susceptible to jack beanα-mannosidase digestion only after removal of Galα1,2- by α-galactosidase. The mode of action of jack bean α-mannosidase (37) supports our assumption that the different sensitivities of H4.2 and H4.3 are due to accessibility of α-linked Man residues. In accordance with this, the underlying structures of other isomers were inferred as well. ASAM, A. saitoi α1,2-mannosidase.