Experiment to detect Pulsed γ-Rays from the Crab Nebula

Converting enzyme activity of free airway cells

The pulmonary circulation was previously shown to inactivate and even activate a number of autacoids. Further studies showed that these enzymatic activities were localized in vascular endothelial cells. The present results shows that guinea pig free airway cells (FACs) convert angiotensin I to angiotensin II and inactivate bradykinin, whereas they do not inactivate serotonin, prostaglandin E2, histamine, and noradrenaline. In the presence of a converting enzyme inhibitor (SQ14225), the angiotensin I was not converted into angiotensin II, but bradykinin was still inactivated, although the speed of inactivation was decreased. Furthermore, when FACs were separated as adherent and nonadherent cells, the cleavage of angiotensin I by adherent cells was similar to that of the total cell suspension. The inactivation of bradykinin was more pronounced in incubation with nonadherent than with the adherent cells. Using selected enzyme inhibitors, we also showed that the conversion of angiotensin by FAC is the result of specific kinase II activity most likely located in macrophages, whereas the bradykinin inactivation is the result of the cooperation of many enzymes including kinase I and II produced by various cell types.

Effect of dithiothreitol of the reaction of renin and angiotensinogen

Effects of several sulfhydryl reagents on the reaction of renin and angiotensinogen were investigated by measuring the production of angiotensin I. Renin and angiotensinogen were prepared from the kidneys of dogs and from plasma of nephrectomized dogs, respectively. The amount of angiotensin I generated was increased with application of dithiothreitol, dithioerythritol and 2,3-mercapto-1-propanol. The greatest enhancement of the generation of angiotensin I was observed with dithiothreitol. Dithiothreitol had no influence on renin activity, on radioimmunoassay for angiotensin I and the recovery of synthetic angiotensin I from the incubation medium. When heterologous angiotensinogen was used, a great enhancement of generation of angiotensin I was observed. Dithiothreitol did not accelerate the reaction following replacement of the natural substrate, angiotensinogen, with the synthetic tetradecapeptide as substrate. It is postulated that dithiothreitol augments angiotensin I generation by acting on the angiotensinogen and not on the renin.