Catalyzes the reversible isomerization of D-mannose to D-fructose (PubMed:33484446). Shows high specific activity towards mannose and fructose, and has no detectable activity towards other monosaccharides and disaccharides (PubMed:33484446). D-mannose = D-fructose Strongly inhibited by Ag(2+), Cu(2+) and cetyltrimethyl ammonium bromide (CTAB). kcat is 0.766 sec(-1) with mannose as substrate. kcat is 0.581 sec(-1) with fructose as substrate. Optimum pH is 7.5. Optimum temperature is 40 degrees Celsius. Thermostable up to 45 degrees Celsius. Monomer. Shows high production efficiency and may be suitable for green production of D-mannose. Belongs to the N-acylglucosamine 2-epimerase family.