An enzyme-coupled assay for glyoxylic acid

Type 2 diabetes risk alleles in PAM impact insulin release from human pancreatic β-cells

The molecular mechanisms underpinning susceptibility loci for type 2 diabetes (T2D) remain poorly understood. Coding variants in peptidylglycine α-amidating monooxygenase (PAM) are associated with both T2D risk and insulinogenic index. Here, we demonstrate that the T2D risk alleles impact negatively on overall PAM activity via defects in expression and catalytic function. PAM deficiency results in reduced insulin content and altered dynamics of insulin secretion in a human β-cell model and primary islets from cadaveric donors. Thus, our results demonstrate a role for PAM in β-cell function, and establish molecular mechanisms for T2D risk alleles at this locus.

Recombinant oxalate decarboxylase: enhancement of a hybrid catalytic cascade for the complete electro-oxidation of glycerol

The complete electro-oxidation of glycerol to CO₂is performed through an electro-oxidation cascade using a hybrid catalytic system combining an organic oxidation catalyst, 4-amino-TEMPO and a recombinant enzyme, oxalate decarboxylase fromBacillus subtilis.

Quantification and mass isotopomer profiling of α-keto acids in central carbon metabolism

Mass spectrometry has been established as a powerful and versatile technique for studying cellular metabolism. Applications range from profiling of metabolites to accurate quantification and tracing of stable isotopes through the biochemical reaction network. Despite broad coverage of central carbon metabolism, most methods fail to provide accurate assessments of the α-keto acids oxaloacetic acid, pyruvate, and glyoxylate because these compounds are highly reactive and degraded during sample processing and mass spectrometric measurement. We present a derivatization procedure to chemically stabilize these compounds readily during quenching of cellular metabolism. Stable derivatives were analyzed by ultrahigh pressure liquid chromatography coupled tandem mass spectrometry to accurately quantify the abundance of α-keto acids in biological matrices. Eventually, we demonstrated that the developed protocol is suited to measure mass isotopomers of these α-keto acids in tracer studies with stable isotopes. In conclusion, the here described method fills one of the last technical gaps for metabolomics investigations of central carbon metabolism.

Effects of salts on aerobic metabolism of Debaryomyces hansenii

Debaryomyces hansenii was grown in YPD medium without or with 1.0 M NaCl or KCl. Respiration was higher with salt, but decreased if it was present during incubation. However, carbonylcyanide-3-chlorophenylhydrazone (CCCP) markedly increased respiration when salt was present during incubation. Salt also stimulated proton pumping that was partially inhibited by CCCP; this uncoupling of proton pumping may contribute to the increased respiratory rate. The ADP increase produced by CCCP in cells grown in NaCl was similar to that observed in cells incubated with or without salts. The alternative oxidase is not involved. Cells grown with salts showed increased levels of succinate and fumarate, and a decrease in isocitrate and malate. Undetectable levels of citrate and low-glutamate dehydrogenase activity were present only in NaCl cells. Both isocitrate dehydrogenase decreased, and isocitrate lyase and malate synthase increased. Glyoxylate did not increase, indicating an active metabolism of this intermediary. Higher phosphate levels were also found in the cells grown in salt. An activation of the glyoxylate cycle results from the salt stress, as well as an increased respiratory capacity, when cells are grown with salt, and a 'coupling' effect on respiration when incubated in the presence of salt.

Physiological ecology of Stenoxybacter acetivorans, an obligate microaerophile in termite guts

Stenoxybacter acetivorans is a newly described, obligately microaerophilic beta-proteobacterium that is abundant in the acetate-rich hindgut of Reticulitermes. Here we tested the hypotheses that cells are located in the hypoxic, peripheral region of Reticulitermes flavipes hindguts and use acetate to fuel their O(2)-consuming respiratory activity in situ. Physical fractionation of R. flavipes guts, followed by limited-cycle PCR with S. acetivorans-specific 16S rRNA gene primers, indicated that cells of this organism were indeed located primarily among the microbiota colonizing the hindgut wall. Likewise, reverse transcriptase PCR of hindgut RNA revealed S. acetivorans-specific transcripts for acetate-activating enzymes that were also found in cell extracts (acetate kinase and phosphotransacetylase), as well as transcripts of ccoN, which encodes the O(2)-reducing subunit of high-affinity cbb(3)-type cytochrome oxidases. However, S. acetivorans strains did not possess typical enzymes of the glyoxylate cycle (isocitrate lyase and malate synthase A), suggesting that they may use an alternate pathway to replenish tricarboxylic acid cycle intermediates or they obtain such compounds (or their precursors) in situ. Respirometric measurements indicated that much of the O(2) consumption by R. flavipes worker larvae was attributable to their guts, and the potential contribution of S. acetivorans to O(2) consumption by extracted guts was about 0.2%, a value similar to that obtained for other hindgut bacteria examined. Similar measurements obtained with guts of larvae prefed diets to disrupt major members of the hindgut microbiota implied that most of the O(2) consumption observed with extracted guts was attributable to protozoans, a group of microbes long thought to be "strict anaerobes."