Table 2.

Processing of wild-type and mutant proMPO

Stably transfected HEK cells expressing wild-type or mutant MPO were radiolabeled biosynthetically, and MPO-related proteins were immunoprecipitated immediately after labeling (at 0 h) and 20 h after chase. Immunoprecipitates were separated by SDS-PAGE. The amount of immunoprecipitated 90- and 59-kDa MPO-related protein at 20 h of chase and the amount of MPO-related protein secreted was quantitated using a phosphorimaging device.

Source	90 kDa:59 kDa (n)a	% Secretedb
Wild-type MPO	0.72 ± 0.08 (13)	100
C319A	1.96 ± 0.27 (5)	28.8 ± 7.9
C158A	1.62 ± 0.24 (6)	5.1 ± 2.0
C158A/C319A	1.64 ± 0.30 (4)	11.9 ± 1.3

^a The ratio of precursor to mature MPO (90 kDa:59 kDa) is shown as mean ± S.E. for n number of experiments. The p values for the differences of 90 kDa:59 kDa for C319A, C158A, and C158A/C319A versus that of wild-type MPO are .0001, .0003, and .0009, respectively.

^b The percent MPO-related protein normalized to that secreted by HEK-MPO cells is shown as the mean ± S.E. for four separate experiments.