A Study of Mimosine Toxicity in Plants

Abstract

Mimosine and 3,4-dihydroxypyridine are inhibitory to the growth of mung bean seedlings. Mimosine inhibition could be reversed by tyrosine or nicotinic acid, but it was reversed by pyridoxal phosphate or ferrous ions. Inhibition due to dihydroxypyridine also could be reversed by ferrous ions, but not by pyridoxal phosphate. The possible mechanisms of growth inhibition are discussed. An enzyme is present in extracts of Leucaena seedlings that degrades mimosine stoichiometrically to 3,4-dihydroxypyridine, pyruvate, and ammonia. An enzymic breakdown of mimosine is also catalysed by extracts of mung bean seedlings. The occurence in Leucaena of dichrostachinic acid and a C-S-Iyase which degrades it to a thiol derivative, pyruvate, and ammonia were described; the latter enzyme was shown to be distinct from the enzyme-splitting mimosine. The substrate specificity, pH optimum, co-factor requirements, and inhibitors of this mimosine C-N-Iyase were investigated.