Faculty Bibliography

The major integral membrane protein of red blood cells, the mouse equivalent of human band 3, was purified and used to raise a specfic antiserum. The murine protein resembles its human counterpart in several of its properties, including susceptibility to digestion by chymotrypsin added to intact cells and an ability to bind to concanavalin A. The synthesis of 35S-labeled band 3 was detected in Friend erythroleukemia cells treated with DMSO by immuneprecipitation followed by SDS gel electrophoresis and fluorography. Induction with DMSO led to a greater than tenfold increase in the synthesis of band 3 and maximal synthesis was reached 3 to 4 days after the beginning of induction

Treatment of rats with phenobarbital leads to a substantial increase in levels of translatable liver cytochrome P-450 mRNA. This mRNA is primarily associated with ribosomes bound to endoplasmic reticulum membranes which in an in vitro system synthesized approximately 10 times more cytochrome P-450 than did free polysomes from the same animals. Cytochrome P-450 synthesized by rough microsomes in vitro appears to be directly inserted into the membranes because it was not released by a treatment with low detergent concentrations that released albumin and other microsomal content proteins. The amino-terminal amino acid sequence of cytochrome P-450 synthesized in an mRNA-dependent system resembles in hydrophobicity the signal segment of presecretory proteins and therefore may serve to insert the polypeptide into the membrane during synthesis. In contrast to the situation with secretory proteins and several other membrane proteins, however, the putative insertion signal of cytochrome P-450 is not removed by a membrane-associated peptidase and remains in the mature polypeptide