Effects of Incubation and Acclimation Temperatures on Incorporation of U-[14C] Glycine into Mitochondrial Protein of Liver Cells and Slices from Green Sunfish, Lepomis Cyanellus

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Abstract
Incorporation of glycine into a sucrose-extracted mitochondrial fraction was measured in liver slices and collagenase-dissociated hepatocytes from green sunfish after acclimation to 5, 15, and 25 C. Incubation temperatures were 10, 15, or 25 C. Liver slices from 5-C-acclimated fish exhibited higher rates of incorporation into mitochondrial protein at 25-C incubation temperature than did slices from 25-Cacclimated animals. However, no apparent differences were observed between 5-C and 25-C acclimation groups at 15-C and 5-C incubation temperatures. Cycloheximide blocked glycine incorporation into the crude mitochondrial fraction of hepatocytes more rapidly than into mitochondria of slices. Collagenase-dissociated hepatocytes and in situ perfused liver exhibited comparable maximal rates of glycine incorporation into the sucrose-extracted mitochondria. Incorporation into slices was approximately one-fourth of that into either hepatocytes or perfused liver. The rate of glycine incorporation into mitochondrial protein of hepatocytes followed apparent Michaelis-Menten kinetics with a of 88.6 μM and a of 11.71 nmol glycine incorporated/mg h⁻¹. At 10-C and 15-C incubation temperatures, incorporation into mitochondrial protein of hepatocytes from 5-C-acclimated fish was significantly greater than for hepatocytes from either 15-C- or 25-C-acclimated fish. No significant differences were observed between these acclimation groups at 25-C incubation temperature. The values of approximately 8.0, 6.0, and 4.0 were obtained for 25-, 15-, and 5-C-acclimated fish, respectively (15-25-C measurement range). It is concluded that incorporation of glycine into a sucrose-extracted mitochondrial fraction shows compensatory acclimation and that hepatocytes from warmacclimated fish exhibit a greater thermal sensitivity for incorporation of glycine into the mitochondrial fraction than do hepatocytes from cold-acclimated fish.