Degradation of methionine by hydrogen peroxide

Hydrogen Peroxide Can Enhance the Synthesis of Bioactive Compounds in Harvested Broccoli Florets

Hydrogen peroxide (H2O2) is a reactive oxygen species (ROS) which participates in the signal transduction responses of plants toward biotic and abiotic stresses. Therefore, the objective of this study was to link the exposure of low doses of H2O2 to the improvement of the phytochemical composition of broccoli florets, in particular the content of glucosinolates (GLS), and hydroxy-cinnamates (HCA) without affecting the quality parameters of the vegetable. A dose of 1.25 mM H2O2 applied for 180 min was effective (hormetic) in maintaining the color of broccoli florets, which was also compared with a higher dose of 5.0 mM H2O2 applied for 180 min. The intensity of the treatments was related to respiration rate, which was monitored for 21 d at 4◦C along to weight loss. The initial respiration rate of florets exposed to both doses of H2O2 was significantly (p < 0.0001) higher relative to controls and resulted in weight loss in florets treated with the hormetic dose. The antioxidant capacity of florets, measured indirectly as Oxygen Radical Absorbance Capacity (ORAC) and ascorbic acid (AA), decreased in florets exposed to both doses. The concentration of glucobrassicins, aliphatic GLS, and HCA was consistently higher in florets treated with the two doses, compared to non-exposed florets. The enhancement of these compounds was accompanied by the over expression, immediately (6 h) after treatments, of tryptophan N-hydroxylase 2 (CYP79B3), dihomomethionine N-hydroxylase (CYP79F1), and phenylalanine ammonia-lyase (PAL) genes. Overall, the tested doses of H2O2 positively influenced the augmentation of indole-type and aliphatic GLS, as well as HCA in broccoli florets.

Chemoenzymatic Production of Enantiocomplementary 2-Substituted 3-Hydroxycarboxylic Acids from L-α-Amino Acids

A two-enzyme cascade reaction plus in situ oxidative decarboxylation for the transformation of readily available canonical and non-canonical L-α-amino acids into 2-substituted 3-hydroxy-carboxylic acid derivatives is described. The biocatalytic cascade consisted of an oxidative deamination of L-α-amino acids by an L-α-amino acid deaminase from Cosenzaea myxofaciens, rendering 2-oxoacid intermediates, with an ensuing aldol addition reaction to formaldehyde, catalyzed by metal-dependent (R)- or (S)-selective carboligases namely 2-oxo-3-deoxy-l-rhamnonate aldolase (YfaU) and ketopantoate hydroxymethyltransferase (KPHMT), respectively, furnishing 3-substituted 4-hydroxy-2-oxoacids. The overall substrate conversion was optimized by balancing biocatalyst loading and amino acid and formaldehyde concentrations, yielding 36-98% aldol adduct formation and 91- 98% ee for each enantiomer. Subsequent in situ follow-up chemistry via hydrogen peroxide-driven oxidative decarboxylation afforded the corresponding 2-substituted 3-hydroxycarboxylic acid derivatives.

Implementation of dietary methionine restriction using casein after selective, oxidative deletion of methionine

Dietary methionine restriction (MR) is normally implemented using diets formulated from elemental amino acids (AA) that reduce methionine content to ∼0.17%. However, translational implementation of MR with elemental AA-based diets is intractable due to poor palatability. To solve this problem and restrict methionine using intact proteins, casein was subjected to mild oxidation to selectively reduce methionine. Diets were then formulated using oxidized casein, adding back methionine to produce a final concentration of 0.17%. The biological efficacy of dietary MR using the oxidized casein (Ox Cas) diet was compared with the standard elemental MR diet in terms of the behavioral, metabolic, endocrine, and transcriptional responses to the four diets. The Ox Cas MR diet faithfully reproduced the expected physiological, biochemical, and transcriptional responses in liver and inguinal white adipose tissue. Collectively, these findings demonstrate that dietary MR can be effectively implemented using casein after selective oxidative reduction of methionine.