Catalyzes the second step in the biosynthesis of pseudaminic acid, a sialic-acid-like sugar that is used to modify flagellin. Uses UDP-2-acetamido-2,6-dideoxy-beta-L-arabino-4-hexulose as substrate producing UDP-4-amino-4,6-dideoxy-beta-L-AltNAc. 2-oxoglutarate + UDP-4-amino-4,6-dideoxy-N-acetyl-beta-L-altrosamine = L-glutamate + UDP-2-acetamido-2,6-dideoxy-beta-L-arabino-hex-4-ulose kcat is 4 min(-1) (PubMed:16286454). kcat is 11.5 min(-1) (PubMed:16690622). Belongs to the DegT/DnrJ/EryC1 family.