KINETIC STUDIES ON AMINO ACID UPTAKE AND PROTEIN SYNTHESIS IN LIVER OF TEMPERATURE ACCLIMATED TOADFISH

¹ Department of Biological Sciences, Hunter College of the City University of New York, 695 Park Avenue, New York, New York 10021
² Marine Biological Laboratory, Woods Hole, Massachusetts 02543

1. A new method is described for measurement of intracellular uptake of amino acids by liver in toadfish (Opsanus tau) in vivo with simultaneous determination of incorporation into aminoacyl transfer RNA and of polypeptide chain assembly time, a kinetic parameter for protein synthesis.

2. Mixed L-amino acids or L-leucine supplied by a pulse injection into the hepatic portal vein are strongly concentrated by liver (up to 75% of dose) compared with D-amino acid or mannitol markers. Uptake occurs against an apparent concentration gradient with halftimes of 15 seconds at 24° and 30 seconds at 11°.

3. The uptake of pulse-injected L-amino acids into intracellular space of liver and the equilibration of the aminoacyl-tRNA pool are rapid compared with the kinetics of polypeptide chain assembly and thus do not interfere with assembly time determination.

4. Polypeptide chain assembly times were 4.0 and 2.5 minutes for warm- and cold-acclimated fish, respectively, at 24° and were 17 and 11.5 minutes for the same groups measured at 11° The Q₁₀ (for acute temperature change) was about 3 for both acclimation groups.