Radiochemical high-performance liquid chromatography methods for the study of branched-chain amino acid metabolism

Simultaneous high-performance liquid chromatography determination of coenzyme A, dephospho-coenzyme A, and acetyl-coenzyme A in normal and pantothenic acid-deficient rats

We describe here a simultaneous high-performance liquid chromatography method for practical and rapid determination of coenzyme A (CoA), dephospho-CoA, and acetyl-CoA in tissues. These coenzymes are biosynthesized from the vitamin pantothenic acid (PaA), which is involved in the metabolism of fatty acids, amino acid catabolism, and several other nutrients. The method employed a Tosoh TSK-GEL ODS-100 V column (250×4.6mm i.d., particle size 5μm) eluted with 100mmol/L NaH(2)PO(4) and 75mmol/L CH(3)COONa (pH was adjusted to 4.6 by the addition of concentrated H(3)PO(4))-acetonitrile (94:6, v/v) at a flow rate of 1.0ml/min. The ultraviolet detector was set at 259nm. The limits of detection for CoA, dephospho-CoA, and acetyl-CoA all were 10pmol. The method was applied to the analysis of several tissues of rats fed normal and PaA-free diets. The results clearly showed that the method was suitable for the simultaneous determination of CoA, dephospho-CoA, and acetyl-CoA in the liver, heart, kidney, spleen, testis, large colon, and muscle, but not for the small intestine, of rats.

Shotgun metabolomics approach for the analysis of negatively charged water-soluble cellular metabolites from mouse heart tissue

A shotgun metabolomics approach using MALDI-TOF/TOF mass spectrometry was developed for the rapid analysis of negatively charged water-soluble cellular metabolites. Through the use of neutral organic solvents to inactivate endogenous enzyme activities (i.e., methanol/chloroform/H2O extraction), in conjunction with a matrix having minimal background noise (9-amnioacridine), a set of multiplexed conditions was developed that allowed identification of 285 peaks corresponding to negatively charged metabolites from mouse heart extracts. Identification of metabolite peaks was based on mass accuracy and was confirmed by tandem mass spectrometry for 90 of the identified metabolite peaks. Through multiplexing ionization conditions, new suites of metabolites could be ionized and "spectrometric isolation" of closely neighboring peaks for subsequent tandem mass spectrometric interrogation could be achieved. Moreover, assignments of ions from isomeric metabolites and quantitation of their relative abundance was achieved in many cases through tandem mass spectrometry by identification of diagnostic fragmentation ions (e.g., discrimination of ATP from dGTP). The high sensitivity of this approach facilitated the detection of extremely low abundance metabolites including important signaling metabolites such as IP3, cAMP, and cGMP. Collectively, these results identify a multiplexed MALDI-TOF/TOF MS approach for analysis of negatively charged metabolites in mammalian tissues.

Synthesis and structure-activity relationship of small-molecule malonyl coenzyme A decarboxylase inhibitors

The discovery and structure-activity relationship of first-generation small-molecule malonyl-CoA decarboxylase (MCD; CoA = coenzyme A) inhibitors are reported. We demonstrated that MCD inhibitors increased malonyl-CoA concentration in the isolated working rat hearts. Malonyl-CoA is a potent, endogenous, and allosteric inhibitor of carnitine palmitoyltransferase-I (CPT-I), a key enzyme for mitochondrial fatty acid oxidation. As a result of the increase in malonyl-CoA levels, fatty acid oxidation rates were decreased and the glucose oxidation rates were significantly increased. Demonstration of in vivo efficacy of methyl 5-(N-(4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropan-2-yl)phenyl)morpholine-4-carboxamido)pentanoate (6u) in a pig ischemia model indicated that MCD inhibitors may be useful for treating ischemic heart diseases.

Separation and quantitation of short-chain coenzyme A's in biological samples by capillary electrophoresis

Because of the importance of coenzyme A's (CoA's or CoASH) in many metabolic processes and the biosynthesis of some carbohydrates and lipids, many methods have been developed to separate and determine their levels in various tissues for metabolism studies, including enzymatic assays, paper chromatography, and high-performance liquid chromatography (HPLC). However, inadequate separation of coexisting CoA's in biological samples was often encountered due to the similarity of their structures. In this paper, we demonstrated for the first time the separation and quantitation of 12 different CoA's by using capillary electrophoresis with UV detection at 254 nm. All 12 CoA's (CoASH, HMG CoA, methylmalonyl CoA, succinyl CoA, methylcrotonyl CoA, isobutyryl CoA, oxidized CoA, acetyl CoA, crotonoyl CoA, n-propzoyl CoA, acetoacetyl CoA, malonyl CoA) were completely separated at -30 kV in a 100 mM NaH2PO4 running buffer containing 0.1% beta-cyclodextrin at pH 6.0. The total separation time was less than 30 min. The signal response was linear over 2 orders of magnitudes (from 1 to 100 nmol), and the detection limits were in the picomole range. The effects of pH, buffer concentration, additives, and operation voltages on sensitivity and resolution were also discussed. This technique, described here, is much more sensitive, faster, and simpler than the published HPLC methods and can potentially be used for mechanistic study in biological systems involving CoA metabolism.

Further insights into the mechanism of action of methylmalonyl-CoA mutase by electron paramagnetic resonance studies

Novel analogues of methylmalonyl-CoA and succinyl-CoA have been prepared and used for mechanistic investigations on the coenzyme-B12-dependent methylmalonyl-CoA mutase. 1-Carboxyethyl-CoA (1) and 2-carboxyethyl-CoA (2) as well as their sulphoxides (3 and 4) were moderately good inhibitors with Ki values 4-20 times higher than the Km for succinyl-CoA. 2-Carboxyethyl-CoA (2) and its sulphoxide 4 induced EPR signals when bound to the enzyme-coenzyme-B12 complex. The EPR spectrum of 2 and its sulphoxide 4 differed very much from those induced by the other substrates. In the case of 2 the EPR spectrum of the holoenzyme/inhibitor complex showed the presence of an organic radical coupled to cobal(II)amin. The same experiment with 4 leads to the formation of enzyme-bound cobal(II)amin with no detectable organic radical. The analogues 1 and 3 exhibited higher Ki values and did not induce EPR signals binding to the enzyme-coenzyme-B12 complex. Formyl-CoA and acrylate inhibited the enzyme synergistically but were unable to induce EPR signals and to form the product. Ethylmalonyl-CoA, known as a poor substrate, induced a similar but less intense EPR signal than the natural substrate methylmalonyl-CoA. The results are discussed in terms of the mechanism of the methylmalonyl-CoA mutase reaction.

Rapid method for the separation and detection of tissue short-chain coenzyme A esters by reversed-phase high-performance liquid chromatography

A simple and rapid method for the separation and identification of tissue levels of short chain coenzyme A (CoA) esters by a reversed-phase high-performance liquid chromatography with ultraviolet-visible adsorbance detection is described. Samples of liver, heart and kidney tissues were homogenised in 5% sulfosalicylic acid containing 50 microM of dithioerythritol in 1:9 w/v proportion. Following centrifugation, 20 microliters of the supernatant were directly injected onto a 3-micron ODS C18 column (100 x 4.6 mm I.D.). The separation of acetyl-CoA, malonyl-CoA, methylmalonyl-CoA, succinyl-CoA, propionyl-CoA and free CoASH was achieved in less than 20 min using gradient elution with sodium phosphate, sodium acetate and methanol at a constant flow-rate of 1.5 ml/min. The lowest detection limit was 3 pmol.

Automated simultaneous isolation and quantitation of labeled amino acid fractions from plasma and tissue by ion-exchange chromatography

In order to trace metabolic pathways of amino acids in the body, a known labeled amount of an amino acid is infused. Dilution in the body pool is measured, using the specific activity and calculated by dividing the labeled amount of an amino acid (tracer) by its total pool (tracer + tracee). This paper describes a method, which combines fractionation and quantitation of multiple amino acids in one chromatographic run. To achieve this, we performed a classical amino acid ion-exchange separation on standard HPLC equipment. The column effluent was divided continuously into two solvent streams using a rapidly switching, pump controlled "split-valve". The main part (90%) was directed to a computer controlled fraction collector, while the remaining 10% was mixed with o-phthaldialdehyde reagent after which fluorescence was measured. Using this system, 10-1000 microliters of deproteinized plasma, representing a maximum of 50 nmol of each amino acid, could be fractionated and quantitated in the same chromatographic run. In addition to optimal counting efficiency of an off-line radioactivity counter, it enabled easy measurement of the specific activity of multiple amino acid tracers.

A radio-enzymatic method for the estimation of L-leucine-specific radioactivity

A method is presented for the estimation of L-leucine concentration and radioactivity in biological samples. The sample L-leucine is specifically bound to tRNA and its radioactivity estimated in the presence of either added labelled L-leucine or cold L-leucine (in the same proportion), as well as in the presence of a large excess of cold L-leucine. The latter gave the measurement of non-leucine radioactivity present in the sample. The measurements in the presence and absence of labelled/cold L-leucine allowed the estimation of L-leucine levels and radioactivity by using a simple set of calculations and a standard curve built with known cold L-leucine concentrations in the presence of a fixed known amount of [14C]L-leucine.

Measurement of the acyl-CoA intermediates of beta-oxidation by h.p.l.c. with on-line radiochemical and photodiode-array detection. Application to the study of [U-14C]hexadecanoate oxidation by intact rat liver mitochondria

The quantitative isolation of acyl-CoA esters of chain length C2-C17 from mitochondrial incubations and their analysis by reverse-phase radio-h.p.l.c. is described. Photodiode-array detection was used to characterize 2-enoyl-CoA esters. The chromatographic behaviour of all 27 intermediates of the beta-oxidation of hexadecanoyl-CoA is documented. Only C16, C14 and C12 intermediates were detected in uncoupled mitochondria oxidizing [U-14C]hexadecanoyl-CoA in the presence of fluorocitrate and carnitine, providing evidence for some organization of the enzymes of beta-oxidation [Garland, Shepherd & Yates (1965) Biochem. J. 97, 587-594; Sumegi & Srere (1984) J. Biol. Chem. 259, 8748-8752]. Rotenone increased concentrations of 3-hydroxyacyl-CoA and 2-enoyl-CoA esters and inhibited flux. These experiments provide the first direct unambiguous measurements of acyl-CoA esters in intact respiring rat liver mitochondrial fractions.

Defects of fatty acid oxidation in skeletal muscle

Fatty acids are important substrates for resting and exercising skeletal muscle. Defects of fatty acid oxidation result in muscle pain and weakness, and there is often lipid accumulation in muscle fibres. Only a few of the several possible enzyme defects have been found and some of these have responded to therapy. Some techniques for the investigation of fatty acid oxidation are outlined.