The ARRHENIUS plot of the specific growth rate p of an asporogenic mutant of Bacillus nlegaterium, growing in the range of 17-37 "C followed a straight line, whose slope was affected by the composition of the medium. The maximal p was found a t 40 "C in all media tested and decreased rapidly above 42 "C. The portion of protein degraded also followed a straight line but reached its maximal value a t 45-47 "C. I t s slope was affected substantially by the composition of the medium; the mixture of amino acids suppressed protein degradation a t temperature lower than 37 "C. The extent of the short-lived protein fraction, degraded with the half-time of about 1 h, was mostly affected by both -the temperature and the medium. The amount of proteins degraded per one biomass doubling was almost constant up to 37 "C but was affected by the composition of the medium. At higher temperatures it increased rapidly and reached values of 20-40% of pulselabelled proteins degraded per one cell cycle. The degradation of ethionine-containing proteins was similarly dependent on the temperature but the extent of proteins degraded was increased.The effect of temperature on protein synthesis and growth is inteiisively studied a t present, because temperature is considered to be an important factor regulating various biological processes (SCHLESINGER et al. 1982 (RATKOWSKY et al. 1982 and1983) tried to overcome this problem by using the square root plot.Within a narrow range around the optimal temperature (Topt, i. e. the temperature of the maximal value of p), the ARRHENIUS plot of p usually deviates from the straight line. One of the factors responsible for this deviation could be an increased protein turnover, which could result in a disharmony between protein synthesis and degradation.The effect of temperature on protein turnover in Escherichia coli was first studied by PINE (1967, 1973). He found that an increased temperature stimulated protein turnover and that the estent of protein degradation in growing and starving populations was similar a t supraoptimal temperatures. The extensive protein turnover at high temperatures might be explained by a recent observation that one of the intracellular proteinases is a heat-shock protein (PHILLIPS et al. 1984). Also in Bacillus megaterium, an increased temperature stimulated the initial rate of protein degradation during growth and sporogenesis. However, a slightly supraoptimal temperature may I ) Participant of the UNESCO Course on Modern Problems in Biology and Biotechnology.
Protein turnover was followed in populations of Bacillus megaterium growing in temperature range of 17-48 degrees C in different media. Higher temperature stimulated the protein turnover (expressed as the amount of protein degraded during 3.3 h) in all the media tested up to the optimal growth temperature (40-42 degrees C). Protein turnover in a medium containing amino acids continued to be stimulated by temperature even above this point; no further significant increase of turnover was found in the other media.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.