STUDY OF GROUND-SQUIRREL MYOGLOBIN - OXIDATION OF GROUND-SQUIRREL MYOGLOBIN BY FERRICYTOCHROME-C

Metmyoglobin (met-Mb) from skeletal muscles of the Yakutian ground squ irrel Citellus undulatus has been isolated and fractionated by gel and ion-exchange chromatography. The main fraction of ground squirrel met -Mb (pI7.05) was obtained with 90% yield. The redox reaction between g round squirrel oxymyoglobin (oxy-Mb) and horse and ground squirrel fer ricytochrome c (Cyt c) was studied in the pH range 5.0-8.0 at ionic st rengths from 0.01 to 1. The results are compared with earlier data of sperm whale and pig myoglobins whose three-dimensional structures and physicochemical properties are well investigated. It is shown that gro und squirrel Mb is very similar in its properties to pig Mb and is dif ferent from whale Mb. The amino acid sequences of about 50 myoglobins from various mammals, birds, and chordates have been analyzed. It is s hown that the rodent myoglobins can be divided in two groups. The myog lobins of animals living in water are similar to Mb of sperm whale and other cetaceans, whereas the myoglobins of ground rodents closely res emble pig Mb. The number of nonhomologous amino acid replacements in e ach of the two groups (1-2 positions) is much smaller than within rode nt myoglobins (8 positions). The charge structure of the Mb contact re gion, which interacts with Cyt c during the electron transfer reaction , is strictly conservative in all mammalian myoglobins analyzed, but n ot in birds and chordates. It is proposed that under some extreme cond itions oxy-Mb can directly interact with cell organelles such as mitoc hondria.