REACTIVE INORGANIC OXY-SPECIES OF C, N, S, AND P - Oxidation of Amino Acids, Peptides, and Proteins: Kinetics and Mechanism - page 241

TABLE 5.8. ( Continued )

Enzyme Modified Residue Reference

Metalloproteinase-4 Trp [343]

Muscle glycogen phosphorylase Tyr [344]

Mitochondrial aconitase glutathione [49]

Mammalian glutamine synthetase Tyr [345]

Microsomal glutathione S-transferase 1 Tyr [346]

a Enzyme in cell extracts, ex vivo or in vivo systems.
b Purified enzyme.
Nd, not determined.

appears the modification of a critical amino acid residue or prosthetic group
resulted from the irreversible inactivation of enzymes (Table 5.8). In some
instances, the loss of activity and modification of amino acids were observed
in vitro and in vivo . For example, peroxynitrite-treated chronically rejected
human renal allograft showed nitration and inactivation of manganese super-
oxide dismutase [321]. Overall, both the reaction rate constants and studies
conducted with cells, extracts, or other biological systems must be taken into
account to learn about the inactivation of enzymes by peroxynitrite.

5.3 SULFUR SPECIES

5.3.1 Oxysulfur Radicals

Sulfur-oxygen radicals SO •− ( n = 3, 4, and 5) are involved in the conversion of
SO 2(g) to acid rain (H 2 SO 4 ). Several studies have therefore been performed to
examine the pathways that result in the SO •− formation and their oxidation
mechanisms [347, 348]. The oxysulfur radicals are also reactive toward biomol-
ecules [347]. Hence, their reactivity toward proteins, dNA, and enzymes has
been carried out [349-351]. In this section, the generation and oxidation mech-
anism of the oxysulfur radicals are described.

5.3.1.1 Generation. The SO 3 radical has been generated by different

methods: (1) oxidation of sulfite with Ce 4+ in acidic solution (Eq. 5.45); (2)
reaction of sulfite produced by Fenton-type reagents, for example, • OH and
• NH 2 ; (3) photoionization of sulfite directly (Eq. 5.46) or through photosensi-
tizers or photolysis of dithionite and thiosulfate; and (4) reaction of sulfite with
radiolytically produced • OH radicals (Eq. 5.47) or other oxidizing radicals
[352]:

• −

Ce

4 +

+ SO

2 −

→ [ Ce

3 +

… SO

−

] Ce

3 +

+

•

SO

−

(5.45)

3 3 3