Zinc endopeptidase with endothelin-3-converting enzyme activity. Cleaves EDN1, EDN2 and EDN3, with a marked preference for EDN3. Binds 1 zinc ion per subunit. Heterodimer with XK; disulfide-linked. Spans the erythrocyte membrane, and is attached to the underlying cytoskeleton. Expressed at high levels in erythrocytes and testis (in Sertoli cells), and, at lower levels, in skeletal muscle, tonsils (in follicular dendritic cells), lymph node, spleen and appendix (at protein level). Also expressed in many adult and fetal nonerythroid tissues, including brain, spleen, lymph nodes and bone marrow. N-glycosylated. KEL is responsible for the Kell blood group system. The molecular basis of the K=KEL1/k=KEL2 blood group antigens is a single variation in position 193; Thr-193 corresponds to KEL2 and Met-193 to KEL1 (PubMed:7849312). The molecular basis of the Kpa=KEL3/Kpb=KEL4/Kpc=KEL21 blood group antigens is a single variation in position 281; Arg-281 corresponds to KEL4, Trp-281 to KEL3 and Gln-281 to KEL21 (PubMed:8669078). The molecular basis of the Jsa=KEL6/Jsb=KEL7 blood group antigens is a single variation in position 597; Leu-597 corresponds to KEL7 and Pro-597 to KEL6 (PubMed:7570911). The molecular basis of the KEL11/KEL17 blood group antigens is a single variation in position 302; Val-302 corresponds to KEL11 and Ala-302 to KEL17 (PubMed:8669078). The molecular basis of the KEL14/KEL24 blood group antigens is a single variation in position 180; Arg-180 corresponds to KEL14 and Pro-180 to KEL24 (PubMed:9354821). Belongs to the peptidase M13 family. Blood group antigen gene mutation database