Identification of a thioredoxin-related protein associated with plasma membranes.

A low molecular weight membrane associated sulphydryl protein was detected on a wide range of nucleated cells when [14C]-iodoacetamide was used as a probe. This protein was extracted from THP-1 monocytes, purified to homogeneity and its isoelectric point, Mr and N-terminal amino acid sequence determined. These were shown to be almost identical to the corresponding values for both human thioredoxin and a Tac interleukin-2 receptor activator, indicating that the protein may be a member of this family and function as an essential growth factor.