Catharacta maccormicki blood samples were collected in the winter (October) and in the summer (February) in order to study the intraerythrocytic organic phosphates, hemoglobin (Hb) electrophoretic patterns, oxygen blood equilibrium and stripped Hbs, as well as the effect of 2,3-biphosphoglycerate (BPG) and inositol hexaphosphate (IHP) on oxygen affinity. All the samples (five from the winter and five from the summer) showed the same electrophoretic pattern: one minor fast component and one major slow one. No differences in oxygen affinity and Bohr effect in the samples collected in the winter and in the summer were found. Oxygen affinity was higher in the stripped Hb than in the blood. BPG seemed to have no effect on the functional properties of skua Hb while IHP does. No BPG was found in any sample. Both inositol pentaphosphate (IP5) and IHP were found in all the samples. The IP5/IHP ratio in the winter samples was 3.0 while in summer 3.5. Adenosine diphosphate (ADP) was found in samples from both the seasons. Adenosine monophosphate (AMP) and adenosine triphosphate (ATP) were present only in the summer samples while guanosine triphosphate (GTP) was found in the winter samples. Since IP5 and IHP are very powerful HB allosteric effectors, ATP and GTP might function as other protein modulators.

Kinetic properties and thermal stabilities of Geophagus brasiliensis skeletal muscle unfractionated malate dehydrogenase (MDH, EC 1.1.1.37) and its isolated isoforms were analyzed to examine a possible sMDH-B* locus duplication in a fixation process influenced by genetic drift. Two optimal pHs were detected: 7.5 for AB1 unfractionated muscle phenotype and its B1 isoform, and 8.0 for AB1B2 unfractionated muscle phenotype, A and B2 isoforms. While G. brasiliensis A isoform could be characterized as thermostable, the duplicated B isoform cannot be assumed as thermolabile. Km values for isolated B2 isoforms were 1.6 times lower than for B1. A duplication event in progress best explains the electrophoretic six-band pattern detected in G. brasiliensis, which would be caused by genetic drift.