Conversion of the Alpha-Hydroxy and Alpha-Keto Analogues of Methionine to Methionine by Cell-Free Extracts of Adult Female Ascaris suum

Abstract

Cell-free extracts of adult female Ascaris suum can convert 2-hydroxy-4-methylthiobutyrate and 2-keto-4-methylthiobutyrate to methionine. The oxidation of the hydroxy analogue utilizes NAD as cofactor which can be partially replaced by NADP. FAD and FMN are inactive. The keto analogue is converted to methionine with the amino group being supplied by glutamate or glutamine. Asparagine and aspartate are partially active but pyridoxamine phosphate does not donate its amino group. The nutritional requirements for and the metabolism of amino acids by parasitic helminths have not been extensively investigated. It has generally been assumed that gastrointestinal helminths have ready access to a full complement of amino acids and use them to satisfy their requirements. The use of the hydroxy analogue of methionine in the diet of the host would then expose the parasite to a new nutritional environment. It was of interest then to determine whether the parasite is able to utilize the analogue as a source of methionine. Data are presented on the metabolic pathway by which cell-free extracts of adult female Ascaris suum convert 2-hydroxy-4-methylthiobutyric acid and 2-keto-4-methylthiobutyric acid to methionine. MATERIALS AND METHODS