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