The propeptide of preprosomatostatin mediates intracellular transport and secretion of alpha-globin from mammalian cells

To determine the intracellular levels of globin-related polypeptides, postnuclear supernatants were adjusted to 1% SDS and incubated at room temperature for 10 rain. 10 vol of buffer A (41) were added followed by addition of 10 #1 of rabbit anti-human hemoglobin antiserum. Samples were incubated at 4°C for 12-24 h with constant mixing (41) . To assay for secreted polypeptides, the medium was adjusted to buffer A conditions by addition of 1/3 vol ofa 4x buffer A solution. Samples were incubated with constant mixing at 4°C for 12-24 h followed by incubation with protein A-Sepharose at 4°C for 3 h (41). Immune complexes were isolated by centrifugation, washed twice with buffer B containing 1 mg/ml BSA (41)