Sulfur amino acids of plants: An overview

Abstract

Publisher Summary This chapter presents an overview of sulfur amino acids of plants. This overview focuses primarily on cysteine and methionine, the major end products of sulfate assimilation. These amino acids comprise up to 90% of the total sulfur of most plants, and are present predominantly (99% or more) in protein. The nonprotein fraction commonly contains glutathione as a major constituent, together with much smaller amounts of sulfur amino acid intermediates involved in protein cysteine and protein methionine biosynthesis (for example, cysteine, cystathionine, homocysteine, and methionine), and in polyamine synthesis and methyl transfer reactions (for example, AdoMet, S-adenosylhomocysteine and 5'-methylthioadenosine). Plants are unusual in that the nonprotein fraction may also contain a variety of sulfur amino acids whose metabolic function and biochemistry have not been clearly defined. Synthesis of cysteine by provides the major portal for organic reduced sulfur compounds in plants. Serine acetyltransferase has been partially purified from plants, and was isolated free of cysteine synthase. The chapter explains the methylation of homocysteine to methionine in plants that is catalyzed by tetrahydropteroyltriglutamate methyltransferase (5-methyltetrahydropteroyltriglutamate-homocysteine methyltransferase).