CHARGE HETEROGENEITY OF MACROPHAGE-MIGRATION INHIBITORY FACTOR (MIF) IN HUMAN LIVER AND BREAST-TISSUE

Macrophage migration inhibitory factor (MIF) is an ubiquitous protein playing various immunological and hormonal roles. Theoretical electrop horetic coordinates calculated from protein sequence in the SWISS-PROT database (AC P14174) are 12 kDa and pI 8.24. Using two-dimensional (2 -D) immunoblotting, we have detected isoelectric forms at ca. 11.9 kDa , with pI values of 7.8 and 6.98 in human liver tissue, breast tissue and a cell line and in preparations of human MIF expressed in E, coli. This evidence suggests that MIF charge heterogeneity originates from a post-translational modification not requiring eukaryote-specific enz ymes. We have also detected in human liver a minor immunoreactive spot at pI 6.23, which coincides with the MIF spot in the liver map in SWI SS-2DPAGE. The pI 6.23 isoform also conceivably derives from posttrans lational modification, as MIF is known to be encoded in the human geno me by a single copy gene.