Initiation by methionine of mouse immunoglobulin light chain containing NH-2terminal pyroglutamic acid
The mechanism of biosynthesis of NH2-terminal pyroglutamic acid has been studied in a mouse plasmacytoma (RPC-20) which produces an immunoglobulin light (lambda) chain containing NH2-terminal pyroglutamic acid. To this end, initation of lambda chain synthesis in plasmacytoma cell suspensions has been investigated. The analysis of radioactive lambda chain synthesis by these cells was accomplished with an antibody preparation specific for the precipitation of lambda chain protein from total plasmacytoma protein. NH2-terminal analysis of plasmacytoma cells labeled with [35S]methionine showed that the ratio of radioactivity in NH2-terminal methionine to total incorporation in lambda chain was greater at 2 min of labeling than at 60 min. However, such a pattern of transient labeling of the NH2 terminus of the lambda chain was not obtained when cells were incubated with tritiated leucine, arginine, or tryptophan. The data indicate that methionine is the initiator amino acid for the synthesis of lambda chain containing NH2-terminal pyroglutamic acid.