Xeragenx human intrinsic factor is a recombinant form (rhIF) that is transgenically expressed in the plant Arabidopsis thaliana. The genetically modified plants have the cDNA encoding mature human intrinsic factor and contain an exact 100% match in its genomic sequence to human IF.
Xeragenx rhIF is the 50 kDa full-length protein, unoccupied as apoIF50 (free of B12 or other bound molecules). After holoIF (B12 bound) is produced as a purified liquid in Step 3 of the Xeragenx Process, it is further processed through a series of proprietary chromatography steps. The rhIF-50 protein is then concentrated by ultra-filtration and subjected to extensive dialysis against the same buffer before being additionally purified by a final gel filtration step.
As can be seen below, the rhIF protein has been shown to bind B12 correctly and in turn bind to the cubilin receptor with as good or better affinity than human IF.
(A) Binding of Cbl and Cbi to recombinant and gastric IF’s
(B) Association and dissociation of IF sources and cubilin