FIGURE 8.

Filtered TIM scans demonstrate Xyl-P-Man₂ and Xyl-P-Man₃ in O-linked glycans from wild-type, xpt1Δ mutant, and XPT1 overexpressing strains. Total ion mapping scans were filtered for the production of MS² fragments that indicate the presence of Xyl-P motifs (panel A, m/z = 573 for Xyl-P-Man₂; panel B, m/z = 777 for Xyl-P-Man₃) in the indicated strains. MS² is inherently more sensitive than full MS for ion-trap instruments, yet the Xyl-P modified glycans are detected as only minor deflections above base line in the xpt1Δ O-linked glycan preparations. The signal traces for KN99α in the left panels and for xpt1Δ pXPT1 in the right panels are displaced upward on the y axis by 5% of full scale for clarity.