Abstract: A DPP-4 inhibitor comprising a peptide represented by the formula (1): Xe-Pro/Ala/Hyp-Xa-Xb-Xc-Xd (SEQ ID NO: 16) (wherein Xe is an amino acid residue with an isoelectric point of 5.9 to 6.3; Pro/Ala/Hyp represents Pro, Ala, or Hyp; Xa is an amino acid residue other than Hyp, Pro, and Arg, or deletion; 5 Xb is Gly, Pro, or deletion; Xc is Pro, Ala, or deletion; and Xd is an amino acid residue or deletion) as an active component. The inhibitor can be expected to bring out an effect of lowering blood glucose levels by enhancing effects of incretins; and the inhibitor may be used as a therapeutic agent for diabetes and, in addition, can act on the immune system or the like to be thus used in 10 treatment for skin diseases or the like.

Abstract: A DPP-4 inhibitor comprising a peptide represented by the formula (1): Xe-Pro/Ala/Hyp-Xa-Xb-Xc-Xd (wherein Xe is an amino acid residue with an isoelectric point of 5.9 to 6.3; Pro/Ala/Hyp represents Pro, Ala, or Hyp; Xa is an amino acid residue other than Hyp, Pro, and Arg, or deletion; Xb is Gly, Pro, or deletion; Xc is Pro, Ala, or deletion; and Xd is an amino acid residue or deletion) as an active component. The inhibitor can be expected to bring out an effect of lowering blood glucose levels by enhancing effects of incretins; and the inhibitor may be used as a therapeutic agent for diabetes and, in addition, can act on the immune system or the like to be thus used in treatment for skin diseases or the like.