Functional molecular size of trypsin inhibitors as determined by radiation inactivation analysis

Minimal functional size of porcine lung and testicular angiotensin-converting enzymes deduced from radiation inactivation analysis. Interaction of two highly homologous domains in somatic isoenzyme

Domain structures of porcine lung and testicular angiotensin-converting enzymes (ACE) were studied by radiation inactivation to test the hypothesis that lung ACE has two catalytic sites localized to discrete, structurally independent domains (the N- and C-domains) of approximately equal size. The minimum functional sizes of lung and testicular ACE, calculated from the inactivation curves obtained, were 140 and 74 kDa, respectively. Since testicular ACE has been demonstrated to contain only the C domain, this result indicates that the two domains in lung ACE are not independent but are, in fact, structurally tightly linked.

Mechanism of activation of particulate guanylate cyclase by atrial natriuretic peptide as deduced from radiation inactivation analysis

The interaction between the receptor (Rc) for atrial natriuretic peptide (ANP) and the effector enzyme particulate guanylate cyclase (GC) has been studied by radiation inactivation. Irradiation of bovine lung membranes produced an increase in GC activity at low radiation doses followed by a dose-dependent reduction at higher doses. This deviation from linearity in the inactivation curve disappeared when lung membranes were pretreated with ANP. Essentially identical results were also obtained with adrenal membranes. Based on these radiation inactivation data, the following dissociative mechanism of activation of particulate guanylate cyclase by ANP has been proposed: Rc.GC(inactive) + ANP----Rc.ANP + GC(active).