219] Oxidative decarboxylation of amino acids (horseradish peroxidase)

Abstract

Publisher Summary This chapter discusses the methods of preparation of oxidative decarboxylation of amino acids (Horseradish Peroxidase). Methionine labeled with 14 C in the carboxyl group is used as the substrate. Radioactive CO 2 is liberated during the reaction and is absorbed in alkali. The amount of 14 CO 2 produced can then be determined by conventional radioactive isotope assay procedures. The pH optimum in sodium phosphate buffer is at 7.0. When collidine or Tris HCI buffers are used, the pH optimum is shifted to a more alkaline value (pH > 8). There is an absolute requirement for Mn 2+ . Other metal ions are ineffective. Pyridoxal-P is required. It can be replaced to some extent by pyridoxal. At the usual concentration pyridoxal is 30% as effective as pyridoxal-P. The addition of phenol or resorcinol (5 × 10 -6 M) gives a 5-fold increase in the total amount of decarboxylation. At the same final concentration chlorogenic acid and caffeic acid inhibit completely, and catechol and hydroquinone give 80% inhibition. Methionine, methionine sulfoxide, alanine, serine, phenylalanine, and tryptophan can all be decarboxylated by this system.