FIGURE 3.

Lack of N-glycosylation enhances ER export of hδOR variants but only the Cys²⁷ variant matures inefficiently. Stably transfected HEK293_i cells expressing WT or non-N-glycosylated mutant receptors were induced for 16 h, pulse-labeled with [³⁵S]methionine/cysteine for 30 min, and chased for the indicated periods of time. Cellular lysates were prepared, and receptors were subjected to two-step immunoprecipitation with FLAG M2 antibody and analyzed by SDS-PAGE, fluorography, and densitometric scanning of the fluorograms. Precursor and mature receptor forms are indicated with open and closed symbols, respectively, and one-N-glycan forms of the WT receptors with an arrow. C and F represent the quantitative analysis of the fluorograms, showing time-dependent changes in the intensity of the labeled receptor forms. The data of the two-N-glycan forms are shown for the WT receptors. The values are means ± S.E. of seven or eight independent experiments, normalized to the corresponding precursor at the end of the pulse.