Abstract
Changes in protein turnover during growth and stationary phase of Natronococcus occultus were studied. The cell capacity for protein synthesis was maximal at the exponential growth phase. This was coincident with increases in both protein/DNA an RNA/DNA ratios. At the onset of exponential growth phase, the synthesis of extracellular protein was higher than that of intracellular protein. Amino acid analysis revealed cells to contain high levels of free glutamic acid (68 to 35 fold higher than free proline), the content of which and total amino groups decreased with growth. Protein breakdown was assessed from the decay of radioactive label. At any growth phase, the half-life of N. occultus bulk protein was shorter than those displayed by eubacteria. Because half-life remained unchanged during lag and early exponential growth phase, the associated increase of cellular protein was ascribed to an increased synthesis. Amino acid composition analysis of bulk protein showed a strong correlation between short half-life and high contents of hydrophobic and acidic amino acids.
Published Version
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