Human renin-binding protein is the enzyme N-acetyl-D-glucosamine 2-epimerase

The existence of human renin-binding protein (RnBP) in the kidney has been shown by the isolation and characterization of a complex of porcine renin-h uman RnBP [S, Takahashi et al, (1985) J, Biochem, 97, 671-677], However, th e properties of the free form of human RnBP had not been understood, becaus e of the limitation of materials. In the present study, we have expressed h uman RnBP in Escherichia coli JM 109 cells under the transcriptional contro l of tag promoter and purified it by conventional column chromatographies. The purified recombinant human RnBP (rhRnBP) exists as a dimer and inhibits porcine renin activity through formation of a complex of porcine renin wit h rhRnBP, the so-called high-molecular-weight renin, Moreover, the rhRnBP c atalyzes the interconversion between N-acetyl-D-glucosamine (GlcNAc) and N- acetyl-D-Mannosamine (ManNAc) with the apparent K-m values of 21.3 mM for G lcNAc and 12.8 mM for ManNAc, and 0.13 mM for effector ATP, ATP is essentia l for the GlcNAc a-epimerase activity of human RnBP, These results indicate that the human RnBP is a GlcNAc 2-epimerase.