CASHON, R/E; HUNT VON HERBING, I: Hemoglobin gelation in boreal fishes: adaptation to the cold?

Recent studies of fish red blood cells found that a regular paracrystalline array of hemoglobin (Hb) tetamers formed under low oxygen conditions in 2 species of boreal fishes, Atlantic cod (Gadus morhua) and toadfish,(Opsanus tau). This phenomenon is termed hemoglobin gelation and its physiological characteristics and importance to survival of boreal fishes is unknown. Preliminary data was obtained on the frequency and physiological nature of the phenomenon of hemoglobin (Hb) gelation in red blood cells of fishes that inhabit cold-water temperate and Arctic environments. Twenty-five species have been examined to date and only the cold-water boreal fishes exhibited Hb gelation. The present study tests the hypothesis that hemoglobin gelation within fish red blood cells may be a feature of normal fish respiratory physiology and might be adaptive in extreme cold-water environments. We will present data on the temperature and pH dependence of gelation and oxygen binding characteristics of purified Hb from in Atlantic cod. Experiments included ligand binding kinetics using stopped flow spectrophotometry, oxygen equilibrium studies using tonometry, and optical microscopy and SEM characterization of Hb crystalline structures. These data test whether if gelation is dependent on the surrounding intracellular matrix. Preliminary findings on purified Hb suggest that gelation is an intrinsic property of the Hb and occurs under conditions which are likely to be found in vivo. The scientific relevance of this is to determine if there are common morphological and physiological traits among hemoglobins of boreal fishes that exhibit gelation and whether these traits are adaptive in extreme environments characteristic of boreal and polar regions.