3-Hydroxyisobutyrate dehydrogenase, an impurity in commercial 3-hydroxybutyrate dehydrogenase

Effects of Workers Exposure to Nanoparticles Studied by NMR Metabolomics

In this study, the effects of occupational exposure to nanoparticles (NPs) were studied by NMR metabolomics. Exhaled breath condensate (EBC) and blood plasma samples were obtained from a research nanoparticles-processing unit at a national research university. The samples were taken from three groups of subjects: samples from workers exposed to nanoparticles collected before and after shift, and from controls not exposed to NPs. Altogether, 60 1H NMR spectra of exhaled breath condensate (EBC) samples and 60 1H NMR spectra of blood plasma samples were analysed, 20 in each group. The metabolites identified together with binning data were subjected to multivariate statistical analysis, which provided clear discrimination of the groups studied. Statistically significant metabolites responsible for group separation served as a foundation for analysis of impaired metabolic pathways. It was found that the acute effect of NPs exposure is mainly reflected in the pathways related to the production of antioxidants and other protective species, while the chronic effect is manifested mainly in the alteration of glutamine and glutamate metabolism, and the purine metabolism pathway.

Characterization of 3-hydroxyisobutyrate dehydrogenase, HIBADH, as a sperm-motility marker

PURPOSE

Asthenozoospermia is a major cause of male infertility. However, the molecular mechanisms underlying sperm-motility defects remain largely unknown in the majority of cases. In our previous study, we applied a proteomic approach to identify unknown proteins that were downregulated in spermatozoa with low motility compared to spermatozoa with good motility. Several sperm motility- related proteins have been identified. In this study, 3-hydroxyisobutyrate dehydrogenase (HIBADH), one of the proteins identified using the proteomic tools, is further characterized.

METHODS

Reverse-transcription polymerase chain reactions (RT-PCR), western blotting, and immunofluorescence assays (IFA) were preformed to investigate the expression pattern. The enzymatic activity of HIBADH was evaluated in sperm with good (>50 %), moderate (< 50 %) and lower motility (< 20 %).

RESULTS

Using RT-PCR, we found that transcripts of HIBADH are enriched in the cerebellum, heart, skeletal muscle, uterus, placenta, and testes of male humans. In western blotting, it is expressed in the placenta, testes, and spermatozoa. During spermiogenesis, HIBADH is located at the mid-piece (a specialized development from the mitochondria) of elongating, elongated, and mature sperm. The enzymatic activity of HIBADH in sperm with moderate and lower motility were significantly reduced compared with good motility (P<0.0001 and P<0.05, respectively).

CONCLUSIONS

Our study indicated that HIBADH is involved in the mitochondrial function of spermatozoa, and maintains sperm motility. It may serve as a sperm-motility marker.

The catalytic property of 3-hydroxyisobutyrate dehydrogenase from Bacillus cereus on 3-hydroxypropionate

The MmsB gene product from Bacillus cereus ATCC14579 exhibits 3-hydroxypropionate dehydrogenase activity. It encodes the 32-kDa enzyme protein composed of 292 amino acids. Recombinant 3-hydroxyisobutyrate dehydrogenase (3-HIBADH) was purified 100-fold from cell extract by ammonium sulfate fractionation and column chromatography. The enzyme catalyzed oxidation of 3-hydroxypropionate (3-HP) between pH 7.0 and 10.0 with optimal activity between 8.8 and 9.0. A Km of 16.8 mM for 3-HP was calculated from a Lineweaver-Burk plot. The semialdehyde as products has been proven by spectrophotometric determination. The dehydrogenase apparently has no metal ion requirement. Kinetic determinations established that 3-HIBADH was more active with NADP(+) than NAD(+), which did not show similarity with previously reported 3-HIBADH except that from Thermus thermophilus.

Biochemical adaptations in the black-tailed prairie dog (Cynomys ludovicianus) during long-term food and water deprivation

1. Glucose and ketone body metabolism was studied in prairie dogs, which can withstand periods of food and water deprivation at near normal body temperatures without apparent utilization of body protein. 2. Plasma glucose concentrations decreased by 18% (from 8.39 to 6.83 mM) when animals were deprived of food and water for 14 days during winter, and 27% (from 7.89 to 5.78 mM) after similar treatment in summer. 3. Glucose utilization rates decreased by 33% (from 41.0 to 27.5 mumol/min/kg) during winter food and water deprivation, but changed little in summer animals (from 26.0 to 21.1 mumol/min/kg). 4. Glucose carbon recycling was 30-31% in winter animals, but essentially zero in summer animals and did not change due to food and water deprivation. 5. Analysis of the fatty acid composition of prairie dog adipose tissue showed no evidence of odd-number carbon fatty acids, a potential source of glucose carbon. No change in adrenal weights were noted. 6. Ketone body concentrations increased 16-fold (from 0.039 to 0.641 mM) after food and water deprivation in the winter, while utilization rates increased 12-fold (from 0.42 to 4.88 mumol/min/100 g). 7. These results are discussed in relation to the ability of the prairie dog to adapt to long-term food and water deprivation.

Pseudoketogenesis in hepatectomized dogs

Overestimation of ketone body turnover in vivo, measured by tracer kinetics, could occur if specific activity or molar percent enrichment is diluted in extrahepatic tissues by label exchange via reversal of 3-oxoacid-CoA transferase, a process we call pseudoketogenesis. To test this hypothesis, euglycemic hepatectomized dogs were injected with a bolus of acetoacetate (0.8 mmol/kg), 32% enriched in [3,4-13C2]acetoacetate. Concentrations and labeling patterns of blood acetoacetate and R-3-hydroxybutyrate were measured by selected ion-monitoring gas chromatography-mass spectrometry. During the 60 min after bolus injection of [3,4-13C2]acetoacetate, the molar percent enrichment of blood [3,4-13C2]acetoacetate decreased to 73 +/- 3% (n = 5) in controls and to 11.5 +/- 0.8% (n = 3) during infusion of dichloroacetate, an activator of pyruvate dehydrogenase. The enrichment of R-3-hydroxy-[3,4-13C2]butyrate followed closely that of [3,4-13C2]acetoacetate. These dilutions occurred despite a net uptake of ketone bodies. Concomitantly, 10.6 +/- 2.2 (n = 5) and 6.0 +/- 2.9% (n = 3) of [13C]acetoacetate molecules were labeled on all four carbons in control and dichloroacetate-treated dogs, respectively. This uniformly labeled acetoacetate arises from partial equilibration between [3,4-13C2]acetoacetate and [1,2-13C2]acetyl-CoA via the reactions catalyzed by 3-oxoacid-CoA transferase and acetoacetyl-CoA thiolase. Our data demonstrate the reversibility of the 3-oxoacid-CoA transferase in intact extrahepatic tissues and support the concept of pseudoketogenesis. This phenomenon has been quantitated by kinetic analysis of the data.

Spectrophotometric enzymatic assay for S-3-hydroxyisobutyrate

An enzymatic spectrophotometric end-point assay has been developed for determination of S-3-hydroxyisobutyrate in biological fluids. The assay measures NADH production at 340 nm after initiation of the reaction with rabbit liver 3-hydroxyisobutyrate dehydrogenase (EC 1.1.1.31). The assay is not affected by R-3-hydroxyisobutyrate, lactate, malate, 3-hydroxybutyrate, 2-methyl-3-hydroxybutyrate, 3-hydroxyisovalerate, 3-hydroxy-n-valerate, 2-methyl-3-hydroxy-valerate, and 3-hydroxypropionate. The assay does measure 2-ethyl-3-hydroxypropionate, a minor metabolite produced by catabolism of alloisoleucine. Application of the method to measure S-3-hydroxyisobutyrate in plasma obtained from normal, 48-h starved, and mildly and severely diabetic rats gave levels of 28, 42, 112, and 155 microM, respectively.

Interference of 3-hydroxyisobutyrate with measurements of ketone body concentration and isotopic enrichment by gas chromatography-mass spectrometry

Concentrations and 13C2 molar percentage enrichments of blood R-3-hydroxybutyrate and acetoacetate are measured by selected ion monitoring gas chromatography-mass spectrometry. Samples are treated with NaB2H4 to reduce unlabeled and labeled acetoacetate to corresponding deuterium-labeled RS-3-hydroxybutyrate species. Only the gas chromatographic peak for the tert-butyldimethylsilyl derivative of 3-hydroxybutyrate needs to be monitored. The various compounds are quantitated using an internal standard of RS-3-hydroxy-[2,2,3,4,4,4-2H6]-butyrate. Concentrations of ketone bodies are obtained by monitoring the m/z 159 to 163 fragments of tert-butyldimethylsilyl derivatives of labeled and unlabeled 3-hydroxybutyrate species. High correlations were obtained between ketone body concentrations assayed (i) enzymatically with R-3-hydroxybutyrate dehydrogenase and (ii) by gas chromatography-mass spectrometry. The limit of detection is about 10 nmol of substrate in blood samples. The current practice of monitoring the m/z 275 to 281 fragments overestimates the concentration of endogenous R-3-hydroxybutyrate, due to co-elution of 3-hydroxyisobutyrate, a valine metabolite. The method presented is used to measure ketone body turnover in vivo in 24-h-fasted dogs.