Catalyzes the interconversion of N-acetylglucosamine to N-acetylmannosamine. Binds to renin forming a protein complex called high molecular weight (HMW) renin and inhibits renin activity. Involved in the N-glycolylneuraminic acid (Neu5Gc) degradation pathway (By similarity). an N-acyl-D-glucosamine = an N-acyl-D-mannosamine Amino-sugar metabolism; N-acetylneuraminate degradation. Homodimer. Belongs to the N-acylglucosamine 2-epimerase family. It is uncertain whether Met-1 or Met-11 is the initiator. Truncated N-terminus.