Abstract
The amino acid sequence of myoglobin from yellowfin tuna (Thunnus albacares) has been determined. The globin is an aminoacetylated chain containing 146 residues and having deletions, with respect to mammalian and avian myoglobins, at the NH2 terminus and two internal locations. From 79 to 85 amino acid substitutions are observed between this myoglobin and those of mammals, birds, and shark. Two external regions containing 6 and 7 residues, which are highly conserved in mammalian and avian myoglobins, are greatly or totally altered in the tuna sequence. Significant differences are apparent in the extent of electrostatic bonding in the myoglobins of fish and in those of mammals or birds.
Highlights
The fish protein differs in length as well, 63 LYS
Herrera has kindly shared with us unpublished data on the bonds is probably related to the greater resistance to autoxisequence of carp myoglobin which showssimilar alterations. dation shown by mammalian myoglobins compared to thatof
It is evident from visual inspection of a commercial three- tuna (14)
Summary
In mammalian and avian myoglobins, are greatly or Materials-The main component myoglobin from the dark muscle totally altered in the tuna sequence. Alkylation of the cysteine sulfhydryl malian sources (5) Exceptions to this include studies of my- was achieved by adding a 20-fold excess of reagent to the protein oglobins from chicken ( 6 ) ,penguin (7), the mollusc Aplysia (typically 2.0 pmol ofMb in 2 ml of 0.1 M sodium pyrophosphate (pH (8), and shark(9).Further exploration of myoglobin sequences from distantly related species may provide insight into the adaptive significance of structural alterations which this protein exhibits. Trypsin digestion of the isolated [5-31] fragment (300nmol in 0.5 d),following removal of the citraconyl blocking group in 5%formic acid during a. Cyanogen bromide cleavage of500 nmol of the isolated [32-132] fragment was carried out in 0.8 ml of 70% formic acid using a 150-fold excess of vacuum-sublimed CNBr for 48 h in an ice bath, following which the mixture was dried in uucuo over NaOH pellets and extracted with 2.5 ml of 10 mM NaHC03 (pH 8.5). (15) andsubjected to amino acid analysis, or subjected to group specific spot tests (19), or high pressure liquid chromatography as described by Bhown et al (20)
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