The Isolation and Examination of Protein Samples of Known Age for the Study of Selectivity of Protein Degradation in Lemna minor

The proposal that the selectivity of protein degradation isdetermined by particular physical properties of proteins hasbeen examined in Lemna minor. A method for isolating proteinof known age is described. Density-labelled proteins of knownage, isolated by the procedure, showed a weak correlation betweenSH content and degradation, and little or no correlation betweenmolecular weight and degradation. An alternative method of examining possible correlations betweenthe rate of degradation of proteins and their physical propertiesis also described. This method which is based on labelling proteinswith ³H₂O gave results suggesting that there was little or nocorrelation between rates of degradation and the molecular weightor charge of proteins. These weak or non-existent correlations are compared with previousreports and lead to the suggestion that the half-life of proteinsis determined by the sum effect of many physical propertiesrather than by a single ‘signal’ property. Key words: Lemna minor, Protein isolation, Protein degradation