The Essentiality of Decyclization of Pyrrolidonecarboxylic Acid Prior to Utilization in Protein Biosynthesis1

the presence of decyclase. The biosynthetic demonstration of PCA decylase in a human plasmacytoma producing a Bence Jones protein with a cyclized glutaminyl amino-terminal residue contrasted to the absence of demonstrable decyclase in a murine plasmacytoma, which was also producing a Bence Jones protein with a cyclized glutaminyl amino terminus. These results indicate a lack of correlation between the presence of PCA decyclase and the occurrence of cyclized glutaminyl as the amino-terminal residue of a polypeptide chain.