OXYGEN-TRANSPORT EFFICIENCY OF MULTIPLE-COMPONENT HEMOGLOBIN IN DAPHNIA-MAGNA

The Adair constants for Daphnia magna hemoglobin (Hb) oxygen equilibri um curves (OECs) were determined, and the fractional oxygen saturation (Y) was differentiated in terms of partial O-2, pressure (p), for Hb- rich (Y-R) and for Hb-poor (Y-p) animals. Y' (dY/dp), which depends on loading and unloading p values of Hb, is used to estimate O-2 transpo rt efficiency. The ratio of the Y' values (Y'(R)/Y'(p)) peaked (2.9) a t a value close to the p(50) Of Hb(R). Using two OECs (Y-I and Y-II) f or monocomponent human adult Hb A, which have similar O-2 affinities t o Hb(R) and Hb(p), respectively, a markedly high ratio of differential coefficients (Y'(I)/Y'(II)) was obtained. It is therefore considered that the occurrence of multiple Hb's showing an inverse correlation be tween Hb concentration and p(50), as in D. magna, minimizes the total Hb concentration required for adaptation to a wide range of O-2 condit ions.