Protein metabolism during germination of Bacillus megaterium spores. II. Degradation of pre-existing and newly synthesized protein.

Two distinct proteolytic systems have been detected during germination of Bacillus megaterium spores: one degrading a unique class of dormant spore proteins and the other degrading primarily protein synthesized during germination. Proteolysis of dormant spore protein began by the 3rd min of germination and by 25 min had degraded 15 to 20% of the pre-existing protein to free amino acids. This reaction was not significantly ( less than 20%) different with or without amino acids or a carbon or nitrogen source in the germination medium, or when RNA synthesis, protein synthesis, or energy metabolism were inhibited. Spore coat proteins and most enzymes were not degraded in this process, rather the major substrates were a unique class of low molecular weight (6,000 to 12,000) proteins which were soluble in acetic acid. Proteins synthesized early in germination (0 to 12 min) were also degraded rapidly (20% per hour). However, proteins synthesized later in germination (90 to 100 min) were degraded more slowly (similar to 4% per hour). At all times tested proteolysis of newly synthesized protein was identical in the presence or absence of amino acids or chloramphenical in the medium, but was abolished by inhibitors of energy metabolism. Most proteins degraded in this process had molecular weights greater than 12,000 and were insoluble in acetic acid.