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Free and Membrane-bound Liver Polysome Patterns of Rats with Different Dietary Intakes of Phenylalanine¹

Department of Biochemistry, Faculty of Science, Laval University, Quebec, Canada

Liver polysome profiles of young rats fed low and high phenylalanine diets were compared to the profiles of their control groups and to control rats fed ad libitum the control diet. The free and membrane-bound ribosomes were studied separately. When rats were kept on low phenylalanine diet for long periods of time the following changes were observed. The free ribosome fraction showed a significant increase in heavy polysomes in the last 20 days of dietary treatment. In the membrane-bound polysomes, on the other hand, there were significant differences in heavy aggregates in the last 20 days of feeding in treated rats and after 10 days in their control group as compared to control animals. There were always less heavy polysomes in these rats compared to the control group. A significant decrease in heavy polysomes was also observed in treated rats. In this case, it is concluded that the synthesis of proteins remaining in the liver was favored over the synthesis of proteins for exportation. In rats fed high phenylalanine diets the following modifications were observed. A significant disaggregation of polysomes in the free ribosome fraction was first produced after 10 days of feeding. After longer treatment there was a progressive increase in heavy polysomes. After 40 days there were significantly more heavy polysomes in the free ribosome fraction of rats fed high phenylalanine than in control rats but significantly less in the membrane-bound fraction of the treated rats than in control animals.

KEY WORDS: • phenylalanine • polysome patterns

¹ Supported by the National Research Council of Canada.

² An Ontario-Quebec exchange fellowship to N. H. is gratefully acknowledged.

Manuscript received 11 September 1972.