The degradation of normal and analogue-containing proteins in MRC-5 fibroblasts

Proteins containing the arginine analogue conavanine were degraded much more quickly in MRC-5 fibroblasts than those containing only normal amino acids. The degradation of both classes of protein could be well described by a pair of exponential curves, the first representing an early rapid degradation and the second, a slower phase. There were no general trends in the variation with passage number of the cell's ability to degrade either normal or analogue-containing proteins, as judged by the half-lives of proteins. But there was an increase in the proportion of labelled normal falling into the early rapid degradation phase as the cells senesced in culture.