Immunoglobulin production stimulating factor-II alpha (IPSF-II alpha) is glyceraldehyde-3-phosphate dehydrogenase like protein.

Amino acid sequence of the 36 KD protein which is the active subunit of immunoglobulin production stimulating factor-II alpha (IPSF-II alpha) 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 erythrocyte, rabbit muscle and Bacillus stearothermophilus also stimulated IgM production of hybridomas, as well as IPSF-II alpha. Conversely, IPSF-II alpha had GPD enzymic activity as strong as rabbit muscle and B. stearothermophilus, and stronger than human erythrocyte GPD. These results suggested that 36 KD subunit of IPSF-II alpha was a GPD, or GPD like protein. The level of mRNA for IgM was not enhanced by IPSF-II alpha in hybridoma cells, though the IgM productivity of the cell was remarkably stimulated by the protein, indicating that IPSF-II alpha does not stimulate immunoglobulin production by enhancement of transcription.