[Study of squirrel myoglobin. Oxidation-reduction reaction between squirrel oxymyoglobin and ferricytochrome c]

Metmyoglobin (met-Mb) of Yakutian ground squirrel (Citellus undulatus) was isolated from skeletal muscles and fractionated using gel and ion-exchange chromatography. An electrophoretically homogeneous major fraction of met-Mb (pI 7.05) was obtained with a 90% yield. The rates of the redox reaction between ground squirrel oxy-Mb and horse and ground squirrel ferri-Cyt c were studied in the pH range of 5-8 at ionic strengths ranging from 0.01 to 1. The experimental results were compared to the earlier obtained data for sperm whale and pig Mbs whose three-dimensional structures and physico-chemical properties are well studied. It was shown that the properties of ground squirrel Mb are very similar to those of pig Mb but differ from those of whale Mb. The amino acid sequences of about 50 Mbs from various mammals as well as from some avian and chordate species (Protein Data Bank) were compared. It was found that rodent myoglobins can be divided into two distinct groups. Myoglobins of animals living in water are identical with those of sperm whale and other cetaceans, while myoglobins of ground rodents closely resemble pig Mb. The number of non-homologous amino acid substitutes in each of the two groups (1-2 positions) is much less compared to all rodent myoglobins (8 positions). The charge structure of the Mb contact site interacting with Cyt c in the course of the electron transfer reaction is strictly conservative for all mammalian Mbs tested in this study (but not for birds and chordates). It is assumed that under certain extreme conditions oxy-Mb can directly interact with cell organelles, such as mitochondria.