ABSTRACT
Two α-actin genes of the fish Leporinus macrocephalus, referring to white and red muscle tissues, were isolated. Actin isoforms, that mainly differed by a Ser/Ala155 substitution, can have a functional significance related to actin-ATP interaction. An Ala155 residue, as observed in the α-skeletal actin from red muscle, results in a decrease in actin's affinity for ATP, which may also be associated to the slow contractile performance of this tissue. Furthermore, a Phe/Ile262 substitution at the red muscle actin leads to a hydrophobicity variation at the D-plug of the protein, which could alter its stability. Data on qRT-PCR evidenced a significant higher actin mRNA level in white muscle when compared to red muscle (T=105 Mann Whitney; p<0.001). This finding could be related to the energetic demands of the white muscle tissue, with fast contraction fibers and glycolytic metabolism for energy supply. Available data on muscle actins lead to the proposal that white and red α-skeletal actins are genetically and functionally distinguishable in fish species, a feature that is not found in other vertebrate groups.
Key words:
ATP interaction; binding site; Ser/Ala155 substitution; Phe/Ile262 substitution
