Modification of proteins in vitro by physiological levels of glucose - Pyridoxamine inhibits conversion of Amadori intermediate to advanced glycation end-products through binding of redox metal ions

Hyperglycemic conditions of diabetes accelerate protein modifications by glucose leading to the accumulation of advanced glycation end- products ( AGEs). We have investigated the conversion of protein- Amadori intermediate to protein- AGE and the mechanism of its inhibition by pyridoxamine ( PM), a potent AGE inhibitor that has been shown to prevent diabetic complications in animal models. During incubation of proteins with physiological diabetic concentrations of glucose, PM prevented the degradation of the protein glycation intermediate identified as fructosyllysine ( Amadori) by C-13 NMR using [ 2-C-13]- enriched glucose. Subsequent removal of glucose and PM led to conversion of protein-Amadori to AGE N-epsilon- carboxymethyllysine ( CML). We utilized this inhibition of post- Amadori reactions by PM to isolate protein- Amadori intermediate and to study the inhibitory effect of PM on its degradation to protein-CML. We first tested the hypothesis that PM blocks Amadori-to- CML conversion by interfering with the catalytic role of redox metal ions that are required for this glycoxidative reaction. Support for this hypothesis was obtained by examining structural analogs of PM in which its known bidentate metal ion binding sites were modified and by determining the effect of endogenous metal ions on PM inhibition. We also tested the alternative hypothesis that the inhibitory mechanism involves formation of covalent adducts between PM and protein-Amadori. However, our C-13 NMR studies demonstrated that PM does not react with the Amadori. Because the mechanism of interference with redox metal catalysis is operative under the conditions closely mimicking the diabetic state, it may contribute significantly to PM efficacy in preventing diabetic complications in vivo. Inhibition of protein- Amadori degradation by PM also provides a simple procedure for the isolation of protein-Amadori intermediate, prepared at physiological levels of glucose for relevancy, to study both the biological effects and the chemistry of post- Amadori pathways of AGE formation

Burning vegetation produces cyanohydrins that liberate cyanide and stimulate seed germination

Cyanide is well known for its toxicity towards living organisms. Many plants use cyanide as a defensive agent against herbivores, releasing it through the enzymatic hydrolysis of endogenous cyanogenic compounds. At low concentrations, cyanide has been proposed to have a regulatory role in many plant processes including stimulation of seed germination. However, no ecological role for cyanide in seed germination has been established. In the present study, we show that burning plant material produces the cyanohydrin, glyceronitrile. We also show that, in the presence of water, glyceronitrile is slowly hydrolysed to release cyanide that stimulates seed germination of a diverse range of fire-responsive species from different continents. We propose that glyceronitrile serves as an ecological store for cyanide and is an important cue for stimulating seed germination and landscape regeneration after fires