Ovoperoxidase activity in ionophore treated mouse eggs. II. Evidence for the enzyme's role in hardening the zona pellucida

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Abstract

<jats:title>Abstract</jats:title><jats:p>One consequence of fertilization or parthenogenetic activation of mammalian eggs is an altaration in the solubility proprieties of the zona pellucida, known as zona hardening. Several lines of evidence indicate that an ovoperoxidase, which is activated and/or secreted from mouse eggs. Following parthenogenetic activation, corss‐links tyrosine residues in the zona pellucida and results in hardening of the zona. First, zona hardening, as determined by decreased solubility of the zona in pronase, is inhibited by several compounds known to inhibit peroxidases. Inhibitors of hardening include phenylhydrazine, sodium sulfite, sodium azide, and glycine ethyl ester. Second, tyrosine analogs inhibit zona hardening, unless the phenolic hydroxyl group or ortho position is blocked. That is, O‐methyltyrosine (methyl substitution of phenolic hydroxyl) does not inhibit hardening; o‐methyltyrosine (methyl substitution of one ortho position) partially inhibits, whereas tyramine and N‐acetyltyrosine (free hydroxyl and ortho positions) effectively block hardening. Finally, exogenous horseradish peroxidasepromotes limited hardening of the zona in unactivated eggs. These results are consistent with a peroxidase catalyzed cross‐linking of tyrosines in the zona that results in hardening of the zona pellucida.</jats:p>

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