BOSWORTH, C.A.*; REES, B.B.: Patterns of protein expression in zebrafish muscle during hypoxia

Alterations of protein expression may be important in determining the capacity of an organism to tolerate low oxygen concentrations. Most previous studies of fish exposed to hypoxia have examined changes in individual proteins. Here, we report on the use of two-dimensional electrophoresis (2DE) to investigate the effects of hypoxia on patterns of global protein expression in the zebrafish, Danio rerio. Zebrafish were held for 48 h in water having a dissolved oxygen concentration of 10% of the air-saturated value, a treatment known to increase the survival time of zebrafish during more severe hypoxia. Proteins from white muscle were solubilized, separated by 2DE, and stained with silver. Among the proteins resolved was a relatively prominent 50 kDa polypeptide that appeared to have at least 2 isoforms differing in isoelectric point (pI). The relative abundance of the 2 forms was altered by hypoxia, with the more basic form predominating in extracts prepared from hypoxic fish. This change in pI is consistent with post-translational modification, perhaps dephosphorylation, of the protein during hypoxia. The polypeptide is similar in size and pI to mammalian pyruvate kinase (PK), an enzyme known to be regulated by reversible phosphorylation. A change in phosphorylation state of zebrafish PK during hypoxia could result in a more active enzyme at physiological substrate concentrations and contribute to an increased capacity for glycolytic ATP generation during hypoxia. Supported by National Science Foundation grant IBN 9723050.