A releationship between protein-degradation rates in vivo, isoelectric points, and molecular weights obtained by using density labelling.

1. Half-lives of five plant enzymes were estimated by rate-labeling with 2H2O on the assumption that loss of catalytic activity is equivalent to protein degradation. 2. This involved measuring band-broadening of activity profiles after isopycnic centrifugation. 3. Isoelectric points were determined by isoelectric focusing, and molecular weights were estimated by gel filtration. 4. The conclusion is drawn from the experimental evidence presented that a weak correlation exists between rates of degradation and isoelectric points (r = 0.699; P greater than 0.10; not significant). 5. A highly significant relationship exists between the logarithm of subunit size and half-life (r = -0.939; P greater than 0.02). 6. A literature survey confirmed the trends observed.