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Sachiko Iwaki-Egawa, Yasuhiro Watanabe, Yasuoki Kikuya, Yukio Fujimoto, Dipeptidyl Peptidase IV from Human Serum: Purification, Characterization, and N-Terminal Amino Acid Sequence, The Journal of Biochemistry, Volume 124, Issue 2, August 1998, Pages 428–433, https://doi.org/10.1093/oxfordjournals.jbchem.a022130
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Abstract
Dipeptidyl peptidase IV (DPP IV) in normal human serum was purified 14, 400-fold with a 25% yield to homogeneity. The molecular weight of the purified enzyme was approximately 110, 000 on SDS-PAGE, almost the same as that of human kidney membrane-bound DPP IV. No difference was found between the two enzymes enzymologically and immunologically, either in substrate specificity, susceptibility to inhibitors, or cross-reactivity with an antirat kidney DPP IV antibody, or in their ability to bind adenosine deaminase. However, the N-terminal amino acid sequence of serum DPP IV lacked the transmembrane domain of the membrane-bound enzyme and started at the 39th position, serine, from the N-terminus predicted from the cDNA nucleotide sequence. These results suggest that membrane-bound DPP IV loses its transmembrane domain upon release into the serum, and that its structure on the plasma membrane is not required for its binding to adenosine deaminase.