Catalyzes the interconversion of N-acetylglucosamine to N- acetylmannosamine (PubMed:10502668, PubMed:12499362, PubMed:9990133). Involved in the N-glycolylneuraminic acid (Neu5Gc) degradation pathway: although human is not able to catalyze formation of Neu5Gc due to the inactive CMAHP enzyme, Neu5Gc is present in food and must be degraded (PubMed:9990133). {ECO:0000269|PubMed:10502668, ECO:0000269|PubMed:12499362, ECO:0000269|PubMed:9990133}. This is the function of ENSG00000102032 (RENBP, renin binding protein).