FIGURE 2.

Fraction of wild type α1 and mutant α1(AD) subunits in heterozygous expression. We depicted the N-terminal amino acids of the mature human (α1^h) and rat (α1^r) α1 subunits (A) with the amino acids numbered starting at the N termini of the signal peptides. The Gln-28 residues are located at the putative N termini of the mature peptides. The full-length mature α1^h and α1^r sequences are identical except that the rat sequence lacks leucine 31 (leucine 4 as numbered from the putative N terminus of the mature peptide). We transfected HEK293T cells with mock vector (negative control, filled histograms) or β2 and γ2 subunits (0.250 μg) and heterozygous α1 subunits in which the sequences of the wild type and mutant subunits were both human or both rat (both_h, both_r, solid lines and gray bars). We also transfected cells with heterozygous receptors in which the sequence of the wild type subunit was human and the mutant subunit was rat (wt_h/AD_r, dashed lines, white bars), and the sequence of the wild type subunit was rat and the mutant subunit was human (wt_r/AD_h, dotted lines, black bars). We stained surface receptors with either the anti-α1^h (B) or α1^r antibody (C) and total receptors with the anti-α1^h antibody (D). We determined the fraction of surface heterozygous subunits composed of wild type subunit by dividing α1^h mean fluorescence in WT^h/AD^r, by the α1^h mean fluorescence in both_h cells (B, 96 ± 3%). We obtained a similar result when we divided α1^r staining in WT^r/AD^h cells by that in both_r cells (C, 92 ± 2%). Similarly, we determined the fraction of mutant subunit in surface heterozygous receptors by dividing α1(AD)^h staining in WT^r/AD^h cells by that in both_h cells (B, 2 ± 0.1%) and dividing α1(AD)^r staining in WT^h/AD^r cells by both_r cells (C, 5 ± 0.4%). In total, heterozygous subunits, the wild type α1^h subunit included 91 ± 4% heterozygous expression and the mutant α1^h subunit included 8 ± 4% heterozygous expression. In both surface and total heterozygous expression, the contribution of the wild type subunit was modestly but significantly (*, p < 0.05) less than 100%.