C. Leeuwenburgh et al., Hydroxyl radical generation during exercise increases mitochondrial protein oxidation and levels of urinary dityrosine, FREE RAD B, 27(1-2), 1999, pp. 186-192
Isolated mitochondria are well-established sources of oxidants in vitro. Th
ere is little direct evidence that mitochondria promote oxidative stress in
vivo, however. Model system studies demonstrate that ortho-tyrosine, meta-
tyrosine, and o,o',dityrosine increase in proteins oxidized by hydroxyl rad
ical. To determine whether mitochondria generate oxidants in vivo, we used
isotope dilution gas chromatography mass spectrometry to quantify levels of
these markers in the heart muscle of control and exercised rats. Exercise
led to a 50% increase in ortho-tyrosine, meta-tyrosine, and o,o'-dityrosine
in the mitochondrial proteins but not cytosolic proteins of heart muscle.
This increase was transient, and levels returned to normal when exercised a
nimals were allowed to rest. There also was a transient increase in the lev
el of o,o'-dityrosine in the urine of exercised rats. This relationship bet
ween mitochondrial and urine levels of o,o'-dityrosine suggests that urine
assays of this oxidized amino acid may serve as noninvasive measures of oxi
dative stress. These observations also provide direct evidence that heart m
uscle mitochondria produce an intermediate resembling the hydroxyl radical
that promotes protein oxidation in vivo. (C) 1999 Elsevier Science Inc.