In vitro protein synthesis by tissues of the fifth instar locust

Abstract

Heart, fat body, and midgut tissues were dissected from fifth instar locusts and incubated in vitro to investigate protein synthesis. The concentration of protein and incorporation of labelled amino-acid was estimated at hourly intervals over a four hour period. Generally the greatest amount of protein was liberated during the first hour of incubation. Following this initial period the amount of protein released into the medium varied, depending on the tissue and the day of the instar on which it was taken from the insect. The incorporation of labelled amino-acid into protein followed a linear pattern. Fat body incorporated the highest levels of radioactive amino-acid into protein. Each tissue showed a characteristic pattern of protein synthesis when the released protein was compared on a day by day basis throughout the instar. The nature of the released protein was investigated by gel electrophoresis. Electropherograms of the released proteins were compared with electrophero grams of haemolymph and tissue homogenates. Some proteins from heart and fat body had the same electrophoretic mobility as haemolymph proteins. Heart tissue was also found to release a phenoloxidase into the incubation medium during the last three days of the instar. Midgut tissue released proteins which were similar to proteins of the midgut lumen, but did not release demonstrable haemolymph proteins.