Estimated half-life
The half life of a protein is the time it takes
for the protein pool of that particular protein to be reduced to the
half. The half life of proteins is highly dependent on the presence
of the N-terminal amino acid, thus overall protein stability
[Bachmair et al., 1986,Gonda et al., 1989,Tobias et al., 1991]. The
importance of the N-terminal residues is generally known as the
'N-end rule'. The N-end rule and consequently the N-terminal amino
acid, simply determines the half-life of proteins. The estimated
half-life of proteins have been investigated in mammals, yeast and
E. coli (see the table
below). If leucine is found N-terminally in mammalian proteins the
estimated half-life is 5.5 hours.
| Amino acid | Mammalian | Yeast | E. coli |
| Ala (A) | 4.4 hour | >20 hours | >10 hours |
| Cys (C) | 1.2 hours | >20 hours | >10 hours |
| Asp (D) | 1.1 hours | 3 min | >10 hours |
| Glu (E) | 1 hour | 30 min | >10 hours |
| Phe (F) | 1.1 hours | 3 min | 2 min |
| Gly (G) | 30 hours | >20 hours | >10 hours |
| His (H) | 3.5 hours | 10 min | >10 hours |
| Ile (I) | 20 hours | 30 min | >10 hours |
| Lys (K) | 1.3 hours | 3 min | 2 min |
| Leu (L) | 5.5 hours | 3 min | 2 min |
| Met (M) | 30 hours | >20 hours | >10 hours |
| Asn (N) | 1.4 hours | 3 min | >10 hours |
| Pro (P) | >20 hours | >20 hours | ? |
| Gln (Q) | 0.8 hour | 10 min | >10 hours |
| Arg (R) | 1 hour | 2 min | 2 min |
| Ser (S) | 1.9 hours | >20 hours | >10 hours |
| Thr (T) | 7.2 hours | >20 hours | >10 hours |
| Val (V) | 100 hours | >20 hours | >10 hours |
| Trp (W) | 2.8 hours | 3 min | 2 min |
| Tyr (Y) | 2.8 hours | 10 min | 2 min |