Deletion of the gene does not affect growth on N-acetyl-D-galactosamine, D-galactosamine or N-acetyl-D-glucosamine. In contrast to E.coli strains C and EC3132, K-12 strains cannot grow on N-acetylgalactosamine and D-galactosamine, because they carry a deletion and thus lack active PTS systems specific for these compounds. Therefore, AgaI in K-12 strains is not involved in the degradation of these compounds. Belongs to the glucosamine/galactosamine-6-phosphate isomerase family. Was originally thought to be involved in the deamination and isomerization of D-galactosamine 6-phosphate to D-tagatofuranose 6-phosphate.