In all tissues, the rates of protein degradation, like rates of protein synthesis, are precisely regulated, and a number of physiological and pathological factors have been shown to alter overall rates of protein breakdown. One key factor is Ca2 In this study, the effect of Ca2 and/or calpain on nNOS degradation was investigated nNOS is a calmodulin-dependent enzyme which generates the free radical second messenger nitric oxide (NO). nNOS was found to contain 4 sequence motifs that are rich in praline (P), glulamic acid (E), serine (S), and threonine (T), called PEST regions. Proteins containing these regions are generally rapidly degraded nNOS present in rat brain 10000 xg supernatant was found to be readily degraded in vitro upon addition of Ca2 in the absence of inhibitors. After 30 mins in the presence of Ca2' nNOS activity typically decreased to about 65% of its original. Western blots showed that degradation of nNOS present in rat brain could be reduced or prevented by EGTA and by the cysteine protease inhibitors, leupeptin and E-64. Purified exogenous calpain was shown to accelerate the degradation of nNOS in the 10000 xg fraction and also degraded purified nNOS. These results suggest that nNOS may serve as a substrate for calpain in vivo, accounting for its rapid degradation (This work was supported by the U.W.I. Campus Research Fund).
|Original language||English (US)|
|State||Published - 1997|
ASJC Scopus subject areas
- Agricultural and Biological Sciences (miscellaneous)
- Biochemistry, Genetics and Molecular Biology(all)
- Cell Biology