SULPHATASE OF OX LIVER .12. EFFECT OF TYROSINE AND HISTIDINE REAGENTS ON ACTIVITY OF SULPHATASE A

The action of several group-specific reagents on sulphatase A has been investigated. Tyrosyl residues are essential (directly or indirectly) for the activity of this enzyme which is inactivated by treatment with N-acetylimidazole or with tetranitromethane, the latter forming eight residues of 3′-nitrotyrosine per molecule of enzyme. Neither SH groups nor amino groups are involved in the reaction catalysed by sulphatase A. Treatment of sulphatase A with acetic anhydride causes a spontaneously reversible inactivation. The acetylated enzyme has a half-life of 90 min at pH 6 which suggests that the inhibition might have been caused by the formation of N-acetylhistidyl residues. The inactivation of sulphatase A by photooxidation in the presence of Rose Bengal would also be consistent with the participation of histidyl residues in the sulphatase reaction but such treatment disrupts the enzyme molecule, as shown by the distribution of its sedimentation coefficient, so that this result cannot be interpreted unambiguously. © 1969.