Changes in the rates of protein synthesis in the brain of goldfish at various temperatures.

Intraperitoneal injections of ¹⁴C] tyrosine suspension into goldfish produced a relatively constant specific activity of free tyrosine in the brain over an 8 hour experimental period. This made the measurement of the rate of cerebral protein synthesis in this time period possible. The increase of protein-bound ¹⁴C] tyrosine was linear with time and occured in most protein fractions. In the absence of a net increase of protein it was an indicator of the rate of cerebral protein turnover. Rates of incorporation of tyrosine into brain proteins were 0.52 per cent/hour at 34° and 0.026 per cent/hour at 10°, i.e., the rate at 34° was about 20-fold that at 10°. Temperature gradients of protein turnover were similar in fish and rat brain.