Functional properties of hemoglobins in the teleost Tilapia grahami

Abstract

The oxygen binding properties ofTilapia grahami hemoglobins have been investigated. The whole blood hemolysate possesses at 35°C a high oxygen affinity (P 50∼ 4.0 mmHg). The O2Hb equilibrium is moderately affected by the ionic strenght chloride concentration) of the hemoglobin solution, while in contrast the temperature sensitivity of the O2Hb equilibrium was very high (ΔH=−20.0 kcal.mole−1). Tilapia hemoglobin separated into 7 main fractions having nearly similar Bohr factors (−0.42<ø<−0.59) in a pH range from 7.2 to 7.6. The Bohr factor andn-value of the composite hemoglobins fell within the range for the individual Hb fractions. Addition of the organic nucleoside triphosphates, ATP and GTP, both occurring inTilapia grahami red cells, caused a marked increase inP 50 as well asn-values, with GTP having an effect nearly twice that of ATP on oxygen affinity. Tilapia grahami lives in conditions of high alkalinity (9.6<pH<10.5), high temperature (T max≅43°C) and variable O2 concentration. The results are discussed in relation to hemoglobin function in this habitat