An electrical potential in the access channel of catalases enhances catalysis

作者：Chelikani P; Carpena X; Fita I; Loewen PC^*

来源：Journal of Biological Chemistry, 2003, 278(33): 31290-31296.

DOI：10.1074/jbc.M304076200

Substrate H2O2 must gain access to the deeply buried active site of catalases through channels of 30 - 50 Angstrom in length. The most prominent or main channel approaches the active site perpendicular to the plane of the heme and contains a number of residues that are conserved in all catalases. Changes in Val(169), 8 Angstrom from the heme in catalase HPII from Escherichia coli, introducing smaller, larger or polar side chains reduces the catalase activity. Changes in Asp(181), 12 Angstrom from the heme, reduces activity by up to 90% if the negatively charged side chain is removed when Ala, Gln, Ser, Asn, or Ile are the substituted residues. Only the D181E variant retains wild type activity. Determination of the crystal structures of the Glu(181), Ala(181), Ser(181), and Gln(181) variants of HPII reveals lower water occupancy in the main channel of the less active variants, particularly at the position forming the sixth ligand to the heme iron and in the hydrophobic, constricted region adjacent to Val(169). It is proposed that an electrical potential exists between the negatively charged aspartate ( or glutamate) side chain at position 181 and the positively charged heme iron 12 Angstrom distant. The potential field acts upon the electrical dipoles of water generating a common orientation that favors hydrogen bond formation and promotes interaction with the heme iron. Substrate hydrogen peroxide would be affected similarly and would enter the active site oriented optimally for interaction with active site residues.

• 出版日期2003-8-15