T. Grune et al., PEROXYNITRITE INCREASES THE DEGRADATION OF ACONITASE AND OTHER CELLULAR PROTEINS BY PROTEASOME, The Journal of biological chemistry, 273(18), 1998, pp. 10857-10862
We report that exposure of aconitase to moderate concentrations of per
oxynitrite, 3-morpholinosydnonimine (SIN-1; a superoxide-and nitric ox
ide-liberating substance), or hydrogen peroxide, inhibits the enzyme a
nd enhances susceptibility to proteolytic digestion by the isolated 20
S proteasome. Exposure to more severe levels of oxidative stress, fro
m these same agents, causes further inhibition of the enzymatic activi
ty of aconitase but actually decreases its proteolytic breakdown by pr
oteasome. It should be noted that the superoxide and nitric oxide libe
rated by SIN-1 decomposition react to form a steady flux of peroxynitr
ite. S-Nitroso-N-acetylpenicillamine, a compound that liberates nitric
oxide alone, causes only a small loss of aconitase activity (25% or l
ess) and has no effect on the proteolytic susceptibility of the enzyme
. Proteasome also seems to be the main protease in cell lysates that c
an degrade aconitase after it has been oxidatively modified by exposur
e to peroxynitrite, SIN-1, or hydrogen peroxide. Using cell lysates is
olated from K562 cells treated for several days with an antisense olig
odeoxynucleotide to the initiation codon region of the C2 subunit of p
roteasome (a treatment which diminishes proteasome activity by 50-60%)
, the enhanced degradation of moderately damaged aconitase was essenti
ally abolished. Other model proteins as well as complex mixtures of pr
oteins, such as cell lysates, also exhibit enhanced proteolytic suscep
tibility after moderate SIN-1 treatment. Therefore we conclude that pe
roxynitrite reacts readily with proteins and that mild modification by
peroxynitrite results in selective recognition and degradation by pro
teasome.