CD26 peptidase activity. The CD26 peptidase activity of sorted Sca-1⁺c-kit⁺lin^— (A) and Sca-1⁺c-kit^—lin^— (B) mBM cells was measured. Using the chromogenic substrate Gly-Pro-pNA, the production of pNA by DPPIV cleavage was monitored. The results are plotted as picomoles pNA produced versus minutes and slope was calculated at the linear portion of the enzymatic curve giving a measure of CD26 peptidase activity expressed as U/1000 cells, where 1 U = 1 pmol pNA/minute. Error bars represent standard errors of the means (SEMs). (A) Sca-1⁺c-kit⁺lin^— mBM cells have CD26 activity (207.97 U/1000 cells, n = 8). (B) Approximately the same peptidase activity was recorded for Sca-1⁺c-kit^—lin^— mBM cells (193.28 U/1000 cells, n = 8).