Protein turnover in growing cultures of Bacillus megaterium

A growing population of Bacillus megaterium, prelabelled with 14C-amino acids displays protein turnover, the rate of which is influenced by the growth rate. The size of the pool of short-lived proteins, degraded with a half-life of less than 1 h, is directly proportional to the mass doubling time during subsequent growth of the population. However, their degradation constant is almost the same under all conditions. The degradation constant of residual long-lived proteins is influenced by the growth rate. The labile fraction can be replenished by a combination of shift-up and shift-down treatments. Tetracycline decreases the size of the labile (short-lived) fraction and almost stops the degradation of long-lived proteins. Correlation of protein turnover and intracellular proteolytic activity indicates that other factors in addition to the proteinase are necessary for the degradation of short-lived, as well as long-lived proteins.