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Coproporphyrinogen oxidase. II. Reaction mechanism and role of tyrosine residues on the activity.

1980; Elsevier BV; Volume: 255; Issue: 10 Linguagem: Inglês

10.1016/s0021-9258(19)85556-4

1083-351X

Tsukasa Yoshinaga, Seiyo Sano,

Neonatal Health and Biochemistry

Purified coproporphyrinogen oxidase catalyzed conversion of 2 -~-h y ~o x ~r o p i o n i c acid-4-propionic acid deuteroporphyrinogen Ix, 2-propionic acid-4-b-h~droxypropionic acid deuteroporphyrinogen DL, 2,4-bisw-hydroxypropionic acid) deuteroporphyrinogen M, harderoporphyrinogen, and isoharderoporphyrinogen to protoporphyrinogen ZX.This result suggests that the enzymatic conversion of propionate groups of coproporphyrinogen I D to vinyl groups of p ~o t o p o r p h ~n ogen IX occurs stepwise starting from position 2 to 4 through /%hydroxypropionate porphyrinogen as an intermediate.When coproporphyrinogen oxidase was treated with tetranitromethane, an initial modification of 1 tyrosine residue per molecule did not affect the enzyme activity, whereas modification of a second tyrosine residue resulted in a substantial inactivation of the enzyme.Conversion of 2,4-bis-@-hydroxypropionic acid) deuteroporphyrinogen IX into protoporphyrinogen IX was not affected by the tyrosine residue modification.Both modification and kinetic studies led to a conclusion that at least one tyrosine residue is involved in the active site of the enzyme, presumably participating in the initial reaction of the oxidation step of a propionate group to fi-hydroxypropionate.