Fig. 4. H₂S is produced by homogenates of bovine pulmonary artery and vein and lamprey dorsal aorta. H₂S production by pulmonary arteries is inhibited by the CBS inhibitor, amino-oxyacetate (AOA; 1 mmol l^–1), the pyridoxyl 5'-phosphate-dependent enzyme inhibitor, hydroxylamine (HA; 1 mmol l^–1), but not by the CSE inhibitor D,L-propargylglycine (PPG; 10 mmol l^–1); HA also inhibits H₂S production in veins. Bovine vessels were pooled from two animals, lamprey aortas were pooled from six fish. Total sulfide (H₂S and HS^–) was measured in triplicate with ion-selective electrodes after alkaline conversion to S^2–. Values are means ± s.e.m.; *significantly different from respective control (P0.05).