Oxygen binding in blood of Xenopus laevis (Amphibia) and evidence against Root effect

Blood oxygen binding was examined in the amphibian, Xenopus laevis, with the particular aim of determining whether the O2 capacity is diminished when blood pH is lowered, which is known as the Root effect in blood of some fishes. Hemoglobin-bound O2 concentration, [O2Hb], was determined by the Lex-O2-Con technique, and both total hemoglobin, [Hb]tot, and Met-hemoglobin, [MetHb], contents were measured spectrophotometrically. From these measurements were calculated the oxygen capacity, O2cap, and the content of active hemoglobin, [Hb]act, i.e. the difference between [Hb]tot and [MetHb]. The main finding was the independence of the ratio of O2cap/[Hb]act on pH, when differences between samples in [Hb]tot and the presence of MetHb, which was particularly pronounced at low pH, where properly accounted for. It is concluded that the Root effect does not exist in blood of the amphibian Xenopus laevis.