THERMOSTABILITY OF FISH HEMOGLOBINS

There are 4 categories of fish Hb thermostability (types I-IV) as measured by the time required for 50% precipitation of a 0.2 g/dl buffered Hb solution at 50.degree. C. T1/2 [half-life] values > 60 min were defined as stable Hb. Type I Hb (skate) was stable at pH 6/0, 7.0 and 8.0; type II (Mustelus canis) was stable at acid pH but unstable at alkaline pH; type III (toadfish) was unstable at acid and stable at alkaline pH; type IV (which includes most fish Hb studied) were unstable at pH 6.0, 7.0 and 8.0. The variable effect of KCl (up to 1.0 M) on thermostability suggested that electrostatic interactions do not contribute uniformly to heat resistance among fish Hb. Alkylureas (0.1-0.3 M) consistently decreased resistance to heat denaturation, for all Hb, in direct relation to alkyl chain length. Hydrophobic interactions may play an important if not primary, role in Hb thermostability.