FIGURE 6.
Plasma kallikrein is the carboxypeptidase/esterase enzyme responsible for tyrosinamide removal from NPY. A, purified plasma kallikrein in phosphate-buffered saline is sufficient to cleave NPY3–36 into NPY3–35. NPY3–35 signal was expressed as the ratio versus porcine NPY1–36 used as internal standard; 1 mg of kallikrein corresponds to an activity of 15 units. One unit is defined as the amount of enzyme that hydrolyzes 1 μmol of d-Pro-Phe-Arg-pNA per min at 25 °C, pH 7.8. B, kallikrein-free plasma is unable to degrade NPY3–36 into NPY3–35. Left panel, NPY3–36 added as a substrate in 10% kallikrein-deficient plasma; middle, 0.5 μg/ml purified kallikrein added in the incubation mix; right, NPY1–36 added as a substrate.