FAPGG hydrolysis proportional to angiotensin I conversion.

<p>A representative ACE activity measurement is shown in <b>A</b>. Decomposition of FAPGG results in a decrease in optical density at 340 nm. The decreases in optical density were plotted as a function of the reaction time and fitted by linear regression. The kinetics of decomposition was followed for at least 90 min. The slope of the linear regression was taken as a measure of the ACE activity. Determinations were repeated at least 3 times to obtain activity values. The ACE activity was also determined by using its endogenous substrate angiotensin I, which is converted to angiotensin II by ACE (<b>B</b>). This reaction was followed by HPLC. Area under the curve was calculated to quantify the amount of the peptides. Calibration plots were constructed based on standard concentrations of the peptides. Angiotensin I conversion was followed by a kinetic assay, where angiotensin I and angiotensin II were determined after 0, 2, 4 and 8 h. The slope of the linear fit gave the ACE activity. A single representative experiment is illustrated (<b>B</b>). Parallel experiments were performed to compare FAPGG and angiotensin I-converting activities of the same sample (<b>C</b>). FAPGG converting activities were plotted as a function of angiotensin I converting activities. Plots were fitted by means of linear regression (solid line), the symbols denote means ± SEM of 3 independent determinations. The goodness of fit (<i>r²</i>) is also indicated on figure.