Immunoglobulin production stimulating factor-IIα (IPSF-IIα) is glyceraldehyde-3-phosphate dehydrogenase like protein

摘要

Amino acid sequence of the 36 KD protein which is the active subunit of immunoglobulin production stimulating factor-IIα (IPSF-IIα) derived from Burkitt's lymphoma Namalwa cells was analyzed for the 20 amino acids from N-terminus. The N-terminal amino acid sequence of this protein coincided very closely with glyceraldehyde-3-phosphate dehydrogenase (GPD; EC 1.2.1.12) derived from various origins. Especially, it was completely homologous with that of human liver GPD. Several GPD's derived from human erythrocytes, rabbit muscle and Bacillus stearothermophilus also stimulated IgM production of hybridomas, as well as IPSF-IIα. Conversely, IPSF-IIα had GPD enzymic activity as strong as rabbit muscle and B. stearothermophilus, and stronger than human erythrocytes GPD. These results suggested that 36 KD subunit of IPSF-IIα was a GPD, or GPD like protein. The level of mRNA for IgM was not enhanced by IPSF-IIα in hybridoma cells, though the IgM productivity of the cell was remarkably stimulated by the protein, indicating that IPSF-IIα does not stimulate immunoglobulin production by enhancement of transcription.