Amino‐Acid Sequences of Heme‐Linked, Histidine‐Containing Peptides of Five Peroxidases from Horseradish and Turnip

Abstract

In a previous paper we have characterized five plant peroxidases, P₁, P₂, P₃ and P₇ of turnip and horseradish isoperoxidase C by peptide mapping studies, and only found two highly homologous sequences present in all. Both contained histidine. The findings supported previous suggestions of two histidine sequences near the peroxidase heme prostetic group. In the present paper we present the amino acid sequences around the histidine residues of all four turnip peroxidases, i. e. of 25 residues around the histidine proximal to heme, and 34 residues around the probably distally located histidine, and compare them with the histidine-containing sequences of the complete amino acid sequence of horseradish isoperoxidase C. Substitutions of residues are rare close to these histidines, but more abundant with greater distances. The probably distal sequences of P₁, P₂, P₃ and horseradish peroxidase C all contain two histidine residues, at positions 40 and 42. In P₇, however, residue 40 is phenylalanine, a substitution presumably important to its abnormal physico-chemical and enzymic properties. Gel filtration profiles of tryptic digests of the turnip isoperoxidases confirm their previous classification into a P₁, P₂ and P₃ group and a distinct P₇ enzyme, but further prove the presence of several sites of carbohydrate attachment in P₁, P₂ and P₃ peroxidases, like in horeseradish peroxidase C which has eight sites. P₇ has one such site.