Regulates and initiates biosynthesis of N-acetylneuraminic acid (NeuAc), a precursor of sialic acids. Plays an essential role in early development (By similarity). Required for normal sialylation in hematopoietic cells. Sialylation is implicated in cell adhesion, signal transduction, tumorigenicity and metastatic behavior of malignant cells. H2O + UDP-N-acetyl-alpha-D-glucosamine = H(+) + N-acetyl-D-mannosamine + UDP an N-acyl-D-mannosamine + ATP = ADP + an N-acyl-D-mannosamine 6-phosphate + H(+) Allosterically regulated (Probable); feedback inhibited by cytidine monophosphate-N-acetylneuraminic acid (CMP-Neu5Ac), the end product of neuraminic acid biosynthesis. Activity is dependent on oligomerization. The monomer is inactive, whereas the dimer catalyzes only the phosphorylation of N-acetylmannosamine; the hexamer is fully active for both enzyme activities (By similarity). Up-regulated after PKC-dependent phosphorylation. Amino-sugar metabolism; N-acetylneuraminate biosynthesis. Homodimer and homohexamer. Highest expression in liver and placenta. Also found in heart, brain, lung, kidney, skeletal muscle and pancreas. Isoform 1 is expressed in heart, brain, kidney, liver, placenta, lung, spleen, pancreas, skeletal muscle and colon. Isoform 2 is expressed mainly in placenta, but also in brain, kidney, liver, lung, pancreas and colon. Isoform 3 is expressed at low level in kidney, liver, placenta and colon. Phosphorylated by PKC. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. In the N-terminal section; belongs to the UDP-N-acetylglucosamine 2-epimerase family. In the C-terminal section; belongs to the ROK (NagC/XylR) family. Truncated N-terminus.