AJP - Regulatory, Integrative and Comparative Physiology, Vol 242, Issue 3 280-R284, Copyright © 1982 by American Physiological Society
L-leucine transport in liver of Antarctic fish in vivo at 0 degrees C
A. E. Haschemeyer
Uptake of L-[14C]leucine by liver of an endemic Antarctic fish, Trematomus
hansoni, was studied by a single injection technique with [3H]inulin as a
reference. Rate constants for leucine influx and efflux and incorporation
into liver protein were determined by analysis of isotope distribution in
the free and protein-bound compartments of liver and in blood draining the
liver at various times after injection. Transport rates were slower than in
temperate fish at 20 degrees C, but saturation properties and ability to
accumulate leucine in liver were comparable. Kinetic analysis indicated
that 30% of uptake at 0 degrees C was due to active transport, similar to
that in toadfish at 20 degrees C. This contrasts with the absence of this
component in toadfish cooled to 10 degrees C. Average polypeptide chain
assembly time was 19 min at 0 degrees C. Transport functions were
maintained in fish warmed to 10 degrees C; however, protein synthesis
declined at temperatures above 5 degrees C. The results indicate this
system is adapted to function at extremely low temperatures in a manner
qualitatively similar to organisms adapted to much higher temperatures.
Transport and synthetic rates, however, were low, consistent with a normal
temperature dependency (Q10 about 2.5) for biological reaction rates.
