Antifreeze Glycoprotein Synthesis in the Antarctic Fish Trematomus hansoni by Constant Infusion in Vivo

Abstract

Synthesis and secretion of antifreeze glycoprotein (AFGP) and other plasma proteins were studied by constant infusion of 14-alanine or 14C-tyrosine in vivo. Both protein classes show an average transit time for secretion of 1 day at −1.5 C; secretion is complete after 4 days. The acid-soluble AFGP accounts for 4% of liver polypeptide synthesis; acid-insoluble plasma protein accounts for 32% of synthesis. Half-life of circulating AFGP is 4 wk, based on the synthetic data. Total alanine incorporation in the secreted proteins was divided about equally between AFGP and the other plasma proteins with specific radioactivity greatest in the AFGP forms eluted earliest from O-(diethylaminoethyl) cellulose (DEAE-cellulose). The various tissues examined showed the following order of protein synthetic activity, based on alanine incorporation: liver > head kidney > stomach, foregut, hindgut > gill, trunk kidney > spleen > heart > red muscle > brain > white muscle. Newly synthesized proteins were examined by sodium dodecyl sulfate (SDS) gel electrophoresis. Tyrosine labeling in liver was concentrated in the 45,000–70,000 mol w t/range, sizes subsequently found in acid-insoluble plasma proteins. Alanine labeling was more broadly distributed over the gels.