The synthesis of freezing-point-depressing protein of the winter flounder Pseudopleuronectusamericanus in Xenpuslaevis oocytes

The serum of the winter flounder $\text{Pseudopleuronectus}$$\text{americanus}$ contains a freezing-point-depressing protein of a molecular weight approximately 10,000 with 60% alanine in its composition. When injected into Xenopus o?cyte, a 6–10 S, poly A-rich RNA preparation isolated from the fish liver polysomes stimulated 3–4 fold the incorporation of [³H] alanine into 10% trichloroacetic acid-soluble, non-dialysable proteins. Analysis of the protein fractions showed a translation product similar in molecular weight and electrophoretic mobility to flounder freezing-point-depressing protein. These observations indicated that the 6–10 S RNA from the flounder contained mRNA for the synthesis of flounder's freezing-point-depressing protein.     

Structural studies on the freezing-point-depressing protein of the winter flounder Pseudopleuronectes americanus

The freezing-point-depressing protein from the winter flounder, $\text{Pseudopleuronectes americanus}$ has been shown from circular dichroism measurements to possess a large proportion (～85%) of the α-helical conformation in aqueous solution (pH 8.0) at ?1°C. The helical content decreases as the temperature is raised. Viscosity data at ?1°C indicate an asymmetric shape for the protein molecule compatible with its high helical content. Thus, the secondary and tertiary structure of this freezing-point-depressing protein as well as its primary structure (reported elsewhere), are found to be different from its counterpart glycoproteins isolated from the Antarctic fish.