Simultaneous Fluorometric Resolution of Pyridoxal, Pyridoxamine and 4-Pyridoxic Acid Using Chemometric Methods

An alternatively minimizing covariant matrix error (AMCME) algorithm, newly proposed by the present authors, was applied to the simultaneous fluorometric determination of pyridoxal, pyridoxamine and 4-pyridoxic acid without loss of sensitivity. The experimental results illustrate that the profiles of spectra and concentration can be accurately resolved using the AMCME algorithm with a high sensitivity and stable repeatability. That is to say, the closely overlapping problem of the spectra could be resolved owing to the characteristic features of the AMCME algorithm.

HPLC study on stability of pyridoxal isonicotinoyl hydrazone

Biocompatible iron chelators are currently under extensive investigation as promising drug candidates. Pyridoxal isonicotinoyl hydrazone (PIH) is a lead compound of the aroylhydrazone group of novel iron chelating agents. In this study, the precise and accurate HPLC analytical methods were used for the stability evaluation of water-soluble PIH salt (PIH x 2HCl) in aqueous media of different pH (2.0, 3.9, 7.0, 9.0 and 12.0) as well as in two selected pharmaceutical co-solvents at both laboratory and elevated (40 degrees C) temperatures. The susceptibility of PIH x 2HCl to oxidative decomposition was studied in the solutions of hydrogen peroxide (3 and 30%). Furthermore, the solid substance of PIH x 2HCl was exposed to UV, dry and wet heat. Our experiments revealed that PIH was considerably sensitive to hydrolytic decomposition in aqueous media, resulting in the splitting of the hydrazone bond. The elevated temperature significantly accelerated the hydrolytic reaction. The lowest rate of hydrolysis of PIH was observed in the phosphate buffer of pH 7.0 and in the pharmaceutical co-solvents (30% PEG-300 and 10% Cremophor EL). No special degradation products were detected in the samples exposed to either hydrogen peroxide or co-solvents. The solid substance of PIH x 2HCl was stable when exposed to UV, dry or wet heat for 33 h.

Chromatographic methods for the separation of biocompatible iron chelators from their synthetic precursors and iron chelates

Chromatographic methods have been developed for the separation of the three novel biocompatible iron chelators pyridoxal isonicotinoyl hydrazone (PIH), salicylaldehyde isonicotinoyl hydrazone (SIH), and pyridoxal 2-chlorobenzoyl hydrazone (o-108) from their synthetic precursors and iron chelates. The chromatographic analyses were achieved using analytical columns packed with 5 microm Nucleosil 120-5 C18. For the evaluation of all chelators in the presence of the synthetic precursors, EDTA was added to the mobile phase at a concentration of 2 mM. The best separation of PIH and its synthetic precursors was achieved using a mixture of phosphate buffer (0.01 M NaH2PO4, 5 mM 1-heptanesulfonic acid sodium salt; pH 3.0) and methanol (55:45, v/v). For separation of SIH and its synthetic precursors, the mobile phase was composed of 0.01 M phosphate buffer (pH 6.0) and methanol (60:40, v/v). o-108 was analyzed employing a mixture of 0.01 M phosphate buffer (pH 7.0), methanol, and acetonitrile (60:20:20, v/v/v). These mobile phases were slightly modified to separate each chelator from its iron chelate. Furthermore, a RP-TLC method has also been developed for fast separation of all compounds. The chromatographic methods described herein could be applied in the evaluation of purity and stability of these drug candidates.

Micellar liquid chromatography in clinical chemistry: application to the monitorization of B6 vitamins

BACKGROUND

A micellar reversed-phase liquid chromatographic procedure was developed for the determination of B6 group vitamins, i.e. pyridoxine, pyridoxal and pyridoxamine, in human serum.

METHODS

Chromatographic conditions used were a C18 column, isocratic mode, flow-rate of 1 ml/min and UV-detection at 290 nm. Optimization of the composition of the mobile phase was performed using an interpretative strategy.

RESULTS

After modeling, the composition of the selected mobile phase was 150 mM sodium dodecyl sulphate (SDS)--2% (v/v) pentanol-dihydrogenphosphate buffer 10 mM at pH 3. In this mobile phase, serum samples were injected without pretreatment and analysis time was below 14 min. Calibrations for the three vitamins were linear, with coefficient regression better than 0.999, and intra- and inter-day precision, achieved according to ICH, offering values below 4.3% and 3.2%, respectively. The method was applied to the determination of the B6 vitamins in spiked serum samples, with recoveries around 100%, and in the pharmacokinetic determination of pyridoxine half-life in serum, which was found to be 47.5 +/- 3.2 min (n = 5). The procedure was also applied for the analysis of pyridoxine in human serum spiked with several pharmaceutical preparations that contain other drugs which do not produce any kind of interference. Finally, solutions of B6 vitamins kept at -201 degrees C are stable for up to 3 months.

CONCLUSIONS

Using the method proposed here, with an SDS-pentanol mobile phase, it is possible to carry out the fast sensitive determination of B6 vitamins in serum following direct injection, without sample pretreatment.

Uptake, hydrolysis, and metabolism of pyridoxine-5'-beta-D-glucoside in Caco-2 cells

An important dietary source of vitamin B-6, pyridoxine-5'-beta-D-glucoside (PNG), exhibits only partial bioavailability, which is limited by the extent of enzymatic cleavage of the beta-glucosidic bond to release metabolically available pyridoxine (PN). This laboratory showed that the intestinal hydrolysis of PNG is catalyzed by cytosolic PNG hydrolase (PNGH) and brush border lactase-phlorizin hydrolase (LPH). LPH-catalyzed PNG hydrolysis in vitro is competitively inhibited by lactose. In the present study, the uptake and hydrolysis of PNG were examined in Caco-2 human colon carcinoma cells, which express a functional LPH but exhibit no PNGH activity. PNG uptake at 37 degrees C was linear over 5-500 micromol/L PNG. Uptake was not significantly reduced when Na(+) was substituted with K(+), Li(+), or Tris in the medium. Increasing PNG concentration in the medium did not change intracellular concentrations of PN, pyridoxamine (PM), pyridoxamine 5'-phosphate (PMP), or pyridoxal 5'-phosphate (PLP); however, intracellular pyridoxal (PL) concentration increased. Intracellular PNG concentration was not significantly reduced in the presence of lactose, but the concentration of PL declined in proportion to extracellular lactose (P = 0.01). These results indicate that PNG can be absorbed intact in a Na(+)-independent process and is taken up by passive diffusion. The presence of lactose in this in vitro model of intestinal uptake reduced the enzymatic hydrolysis of PNG by lactase.

Vitamin B-6 content of breast milk and neonatal behavioral functioning

OBJECTIVE

To determine if vitamin B-6 intakes of mothers influence the B-6 vitamer content of transition milk and if correlations exist between the vitamin B-6 content of the milk and the infants' neurobehavioral functioning.

DESIGN

Transition milk samples were collected from mothers 8 to 11 days after delivery for B-6 vitamer analysis. Neurobehavioral functioning of the neonates was determined at that time. A 24-hour recall was used in estimating vitamin B-6 intakes of the mothers.

SUBJECTS

A convenience sample of low-income, lactating women (n = 25) who had normal pregnancies.

MAIN OUTCOME MEASURES

B-6 vitamers were measured in the mothers' transition milk samples. Neurobehavioral functioning was assessed using the Brazelton Neonatal Behavioral Assessment Scale (NBAS), and the Center for Epidemiologic Studies Depression Scale was used to evaluate maternal depression.

STATISTICAL ANALYSES PERFORMED

Pearson correlation coefficients were used to assess if statistically significant relationships existed between variables. The Mann-Whitney test was used to determine if median group values were significantly different.

RESULTS

The major B-6 vitamer in transition milk was pyridoxal. Mothers with vitamin B-6 intake greater than the median value had a significantly higher median pyridoxal level in their breast milk than did the mothers with intakes below the median value. All except one mother had a dietary vitamin B-6 intake that exceeded the Recommended Dietary Allowance. Infant scores on habituation (r = .94, P < .05) and autonomic stability (r = .34, P < .05) subscales of the NBAS were positively correlated with milk pyridoxal values.

APPLICATIONS/CONCLUSIONS

Vitamin B-6 is important for normal behavioral functioning of infants. The mothers' vitamin B-6 intake affects vitamin B-6 levels of breast milk and the need for consuming recommended levels of vitamin B-6 should be emphasized to all pregnant and lactating mothers.

Differential scanning calorimetry and scanning thermal microscopy analysis of pharmaceutical materials

Micro-thermal analysis (microTA) by scanning thermal microscopy is being used increasingly for the analysis of pharmaceutical dosage forms. However, there is currently little evidence to show that microTA data can compare directly with that from the established approach of differential scanning calorimetry (DSC). This work compares DSC and microTA data from an active vitamin B6 analogue, pyridoxal hydrochloride, and two commonly used pharmaceutical excipients, Mannitol and Avicel which are used in its formulation. It is found that microTA provides precise and accurate micro-thermal analytical data with 0.1 K thermal sensitivity, which is comparable to that obtained by DSC measurements of bulk samples. It is also shown that microTA offers the opportunity to study single particles and the interfacial region between particles, data which is currently inaccessible through the DSC technique.

An enzymatic fluorometric assay for pyridoxal with high specificity and sensitivity

An enzymatic fluorometric assay for pyridoxal with pyridoxal dehydrogenase was developed. The detection limit was about 10 pmol: the calibration curve of pyridoxal showed high linearity (r=0.993). The values obtained by this method correlated well with those by the HPLC method. The enzyme had a high specificity for pyridoxal, and thus animal samples could be directly analyzed without separation of pyridoxal 5'-phosphate by column chromatography.

Effect of phosphate on stability of pyridoxal in the presence of lysine

The stability of the biologically active compound vitamin B(6) in aqueous solution was investigated. Schiff base formation is the major reaction between the epsilon-amino group of lysine and the aldehyde group of both pyridoxal and pyridoxal phosphate. Model systems composed of equal molar concentrations of lysine with either pyridoxal or pyridoxal phosphate were used to study the effect of proton transfer on Schiff base formation. Pyridoxylidenelysine was found to be the major product in both lysine/pyridoxal and lysine/pyridoxal phosphate systems. Quantitation of residual pyridoxal and pyridoxal phosphate was conducted using an HPLC to evaluate the degradation of pyridoxal and pyridoxal phosphate. The results indicate both the free phosphate ion in the buffer system and the bound phosphate on pyridoxal phosphate can enhance the formation of the Schiff base. The phosphate group serves as both proton donor and acceptor, which catalyzes the Schiff base formation. The aldehyde group on pyridoxal phosphate was found to be much more reactive than that on pyridoxal. The bound phosphate group on pyridoxal phosphate, with proton donating and accepting groups in close proximity, can simultaneously donate and accept protons, thus enhancing Schiff base formation between the aldehyde group and the epsilon-amino group. The deterioration rate of pyridoxal phosphate was faster than that of pyridoxal in an aqueous system.

Determination of vitamin B(6) in cooked sausages

A reverse-phase high-performance liquid chromatography (HPLC) method has been described for the determination of various active forms of vitamin B(6) in meat products. Different extracting agents were tested to solubilize fully the analyte for quantification. The best data were obtained by extracting the samples with 5% (w/v) metaphosphoric acid. Separation by HPLC was performed with fluorescence detection (excitation, 290 nm; emission, 395 nm), on a 10 cm x 0.46 cm i.d. Hypersil BDS C(18) 5 microm column using a mixture of 50 mM phosphate buffer (pH 3.2) and acetonitrile (99:1, v/v) as mobile phase. Precision of the method was 0.5% (within a day) and 4.3% (between days). The detection limits were 0.020 mg/100 g for pyridoxal and pyridoxamine, 0.017 mg/100 g for pyridoxamine phosphate, 0.500 mg/100 g for pyridoxal phosphate, and 0.033 mg/100 g for pyridoxol, with a signal-to-noise ratio of 3. The recovery ranged from 92.0 to 100.0%.

Determination of vitamin B6 (pyridoxamine, pyridoxal and pyridoxine) in pork meat and pork meat products by liquid chromatography

A liquid chromatographic method for determining vitamin B6 compounds in pork meat and pork meat products is examined. It uses the same extraction procedure as that applied for thiamin and riboflavin determination, followed by a liquid chromatographic separation on a reversed-phase C18 column with 0.01 M H2SO4 as mobile phase at 30 degrees C. 4-Deoxypyridoxine is used as internal standard. The analytical parameters linearity, precision of the method (R.S.D. = 7.3 and 6.9% for pyridoxamine and pyridoxal, respectively) and accuracy obtained by recovery assays (99 and 85.1% for pyridoxamine and pyridoxal, respectively) show that the studied method is useful to measure these compounds in pork meat.

[The effect of different vitamin B6 supplies on the vitamin B6 status (pyridoxine, pyridoxal and pyridoxamine) of the liver and the body of lactating rats]

Eighty female Sprague-Dawley rats were fed a semisynthetic diet during gravidity which was supplemented with 5 mg vitamin B6 per kg diet. The daily food intake was 14 g. During the following lactation the rats were assigned to one of 10 vitamin B6 treatment groups (0, 3, 6, 9, 12, 15, 18, 36, 360 and 3,600 mg per kg diet). The feed was given ad libitum. At day 14 of lactation the rats were decapitated. Parameters for determination of the vitamin B6 status were concentration of pyridoxine, pyridoxal and pyridoxamine in liver and body analyzed by using HPLC. Body was defined without the gastroenteral tract that was divided into carcass (extrahepatic compartments without liver) and total body (extrahepatic compartments plus liver). The mean weight of liver was 13 g with a dry mass of 33%; there was no difference between the treatment groups. The vitamin B6 concentration was lowest in rats fed 0 mg vitamin B6/kg diet (5 micrograms/g fresh matter, FM) and highest in the rats fed 3600 mg vitamin B6/kg diet (10.9 micrograms/g FM). The total vitamin B6 consisted on the average of 38% pyridoxal and 62% pyridoxamine. This was only changed significantly at the highest supplementation level, where 20% pyridoxine were detected instead of pyridoxamine. The mean weight of carcass averaged 212 g at a dry matter content of 31%. The vitamin B6 concentration ranged in the treatment groups from 0 mg to 360 mg vitamin B6/kg diet between 2.1 micrograms/g FM and 2.8 micrograms/g FM. It was highest in the 3600 mg vitamin B6 treatment group at 7.5 micrograms/g FM. The total vitamin B6 consisted of 63% pyridoxal and 37% pyridoxamine. It was only significantly affected in the 3600 mg vitamin B6 treatment group, where also pyridoxine could be found in the amount of 56%. The results indicate that alimentary vitamin B6 supply had more influence on liver vitamin B6 concentration than on carcass concentration. Total body concentration is very similar carcass concentration, as 95% of vitamin B6 is located there. The suitability of the parameters by the evaluation of the vitamin B6 requirement was confirmed the comparison of two statistical methods. It is concluded that a vitamin B6 supply of 5 to 6 mg/kg diet is necessary to meet the requirements during lactation.

Tissue B-6 vitamer concentrations in rats fed excess vitamin B-6

Diets containing 1, 10, 100, 175 or 250 times the NRC recommended level of pyridoxine HCl (7 mg/kg) were fed to rats (218 g, 12 per group) to evaluate the effects on tissue B-6 vitamer concentrations. After 10 wk, food intake and body weights did not differ among groups. Overt toxicity was not observed. Tissues were taken from five rats of each group after overnight food deprivation (unfed rats); the remaining seven rats in each group were allowed access to food (fed rats). In plasma of unfed rats, 4-pyridoxic acid and pyridoxal concentrations increased significantly (P < 0.05) with increasing dietary pyridoxine; pyridoxal phosphate was not affected by dietary pyridoxine. Concentrations of pyridoxal phosphate and pyridoxal increased significantly with increasing dietary pyridoxine in erythrocytes of unfed rats. Excretion of urinary B-6 vitamers and 4-pyridoxic acid in a 24-h period increased with dietary pyridoxine in fed rats. As dietary pyridoxine was increased, kidney pyridoxal concentrations increased significantly in fed rats only. Dietary pyridoxine did not affect vitamer concentration in muscle and liver of either unfed or fed rats, or in brain of unfed rats. Muscle glycogen phosphorylase, which contains pyridoxal phosphate, was not affected by dietary pyridoxine. There was a marginally significant (P = 0.058) increase in erythrocyte alanine, but not in aspartate, aminotransferase activity with increasing dietary pyridoxine. Plasma concentration of pyridoxal phosphate, which is used as a measure of vitamin B-6 status, did not reflect intake of pyridoxine in this study.(ABSTRACT TRUNCATED AT 250 WORDS)

A fluorometric assay for pyridoxal kinase applicable to crude cell extracts

We have developed an assay for pyridoxal kinase which takes advantage of the intense fluorescence yield of the oxime of pyridoxal or pyridoxal-5'-phosphate and the substantial difference in the rates of formation of these two oximes. Evidence is presented which demonstrates that the assay is linear with respect to time and amount of protein and is applicable to the activity in crude cell extracts as well as purified enzyme.

[Determination of water-soluble vitamins B1, B2, B6 and B12 in milk using HPLC]

Simple methods of determining the water-soluble vitamins B1, B2, B6 and B12 in milk by HPLC are described. Compared to existing procedures, the following improvements can be realized. The oxidation of vitamin B1 to thiochrome is stopped by the addition of sodium sulphite. This step significantly increases repeatability. Thiochrome is then extracted with butan-1-ol, which results in fewer co-extracts and greater selectivity. After the hydrolysis of the 5-phosphates of the vitamin B6 (pyridoxine, pyridoxal and pyridoxamine), these three vitamers are determined by isocratic HPLC as DDS-ion-pairs and with fluorimetric detection. As only microbiological methods have so far been used for the determination of minute quantities of vitamin B12 in milk, a new HPLC procedure is proposed with a detection limit of 0.2 micrograms vitamin B12/L milk.

Determination of vitamin B6 vitamers and pyridoxic acid in biological samples

For the determination of vitamin B6 vitamers (pyridoxal phosphate, pyridoxamine phosphate, pyridoxal, pyridoxine, pyridoxamine) and 4-pyridoxic acid in biological samples such as plasma, cerebrospinal fluid and rat brain regions, a sensitive micromethod using high-performance liquid chromatography (HPLC) with fluorescence detection in combination with post-column derivatization is described. Metaphosphoric acid tissue extracts with deoxypyridoxine as an internal standard were injected into the HPLC system with a binary gradient elution at a flow-rate of 1.2 ml/min. The excitation wavelength of the fluorescence detector was set at 328 nm and the emission wavelength at 393 nm with a 15-nm slit width for the photocell. This method allows the assay of vitamin B6 vitamers within 30 min in one chromatographic run. The present method has been applied extensively for the measurement of vitamin B6 vitamer levels in discrete brain regions of small animals, cells in culture and biopsy samples.

Characterization and sequencing of the active site of 1-aminocyclopropane-1-carboxylate synthase

The pyridoxal phosphate (PLP)-dependent 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (S-adenosyl-L-methionine methylthioadenosine-lyase, EC 4.4.1.14), the key enzyme in ethylene biosynthesis, is inactivated by its substrate S-adenosylmethionine (AdoMet). Apple ACC synthase was purified with an immunoaffinity gel, and its active site was probed with NaB3H4 or Ado[14C]Met. HPLC separation of the trypsin digest yielded a single radioactive peptide. Peptide sequencing of both 3H- and 14C-labeled peptides revealed a common dodecapeptide of Ser-Leu-Ser-Xaa-Asp-Leu-Gly-Leu-Pro-Gly-Phe-Arg, where Xaa was the modified, radioactive residue in each case. Acid hydrolysis of the 3H-labeled enzyme released radioactive N-pyridoxyllysine, indicating that the active-site peptide contained lysine at position 4. Mass spectrometry of the 14C-labeled peptide indicated a protonated molecular ion at m/z 1390.6, from which the mass of Xaa was calculated to be 229, a number that is equivalent to the mass of a lysine residue alkylated by the 2-aminobutyrate portion of AdoMet, as we previously proposed. These results indicate that the same active-site lysine binds the PLP and convalently links to the 2-aminobutyrate portion of AdoMet during inactivation. The active site of tomato ACC synthase was probed in the same manner with Ado[14C]Met. Sequencing of the tomato active-site peptide revealed two highly conserved dodecapeptides; the minor peptide possessed a sequence identical to that of the apple enzyme, whereas the major peptide differed from the minor peptide in that methionine replaced leucine at position 6.

Analysis of B-6 vitamers in human milk by reverse-phase liquid chromatography

A simple, accurate reverse-phase high performance liquid chromatography (RPLC) method was introduced for the analysis of B-6 vitamers in human milk. The assay consisted of a phosphate buffer (pH 2.9) delivered isocratically through 5 micron ODS column packing, followed by post-column bisulfite derivatization to enhance the detection of PLP (and to a minor extent PL). The vitamers were detected using a fluorescence spectromonitor. Sample run time was less than 30 min. The sensitivity of the method was such that PL, PN, and PLP were detectable to 30 pmol/ml milk and PM and PMP to 5 pmol/ml milk. Total vitamin B-6 content in milk analyzed by RPLC correlated well with the microbiological assay. B-6 vitamer distribution in human milk was similar to values obtained from two different ion-exchange HPLC systems. The RPLC procedure is simpler and faster than the HPLC systems and is suggested for future use in analysis of B-6 vitamer concentrations in human milk.

Quantities of B6 vitamers in human milk by high-performance liquid chromatography. Influence of maternal vitamin B6 status

A rapid, sensitive procedure is described for the analysis of the B6 vitamers pyridoxal, pyridoxamine, and pyridoxine in human milk from women taking and not taking supplements containing the vitamin using high-performance liquid chromatography with fluorometric detection. Vitamer values represent the sum of their phosphorylated and unphosphorylated forms. Minimum detectable quantities were 1-3 ng. Excellent recoveries of these vitamers in milk were obtained. Similar B6 vitamer concentrations of milk were obtained using the developed high-performance liquid chromatographic and the accepted microbiological techniques. Pyridoxal, actually consisting of pyridoxal plus pyridoxal phosphate, was the predominant B6 vitamer in human milk. The concentration of B6 vitamers in milk was reflective of the maternal vitamin B6 status.

A high-performance liquid chromatography assay for asparagine synthetase

A highly sensitive method for assaying asparagine synthetase and its glutaminase activity is presented. The amino acids L-asparagine, L-aspartate, L-glutamate, and L-glutamine, are separated by derivatization with o-phthaldialdehyde followed by reversed-phase high-performance liquid chromatography on an Altex ultrasphere-ODS C18 column. The elution is isocratic and the mobile phase used is 50 mM sodium acetate buffer (pH 5.9) with 30% methanol. This assay can easily detect picomoles of asparagine, which may be difficult to do with the other assays that have been described.

Relative activity of the nonphosphorylated B-6 vitamers for Saccharomyces uvarum and Kloeckera brevis in vitamin B-6 microbiological assay

Accuracy in the microbiological assay of vitamin B-6 is dependent, in part, on equivalent response to each form of the vitamin by the assay organism. Recently, Kloeckera brevis (ATCC 9774) has been suggested as an alternative to Saccharomyces uvarum (ATCC 9080) because of its reported equivalent response to pyridoxine (PN), pyridoxal (PL), and pyridoxamine (PM) in turbidimetric yeast growth assays. Evaluation of the merits of these yeasts in our laboratory yielded contrasting results. As widely reported, S. uvarum exhibited greater growth response with PN than with equivalent molar concentrations of PL or PM. K. brevis exhibited an even greater disparity. Pronounced concentration dependence was observed for the response differences among vitaminers with each organism. On the basis of the variable specificity of K. brevis, this organism is not preferable to S. uvarum for the microbiological determination of total vitamin B-6.

The purification and properties of urocanase from Pseudomonas testosteroni

Urocanase (urocanate hydratase, EC 4.2.1.49) purified from Pseudomonas testosteroni has a mol.wt. of 118000 determined by sedimentation-equilibrium analysis. Ultracentrifugation in 6M-guanidine hydrochloride and polyacrylamide-gel electrophoresis in sodium dodecyl sulphate show that the enzyme consists of two identical or very similar subunits. It is, like urocanase isolated from other sources, inhibited by reagents that react with carbonyl groups. Although urocanase from Ps. testosteroni is strongly inhibited by NaBH4, no evidence could be obtained for the presence of covalently bound 2-oxobutyrate as a prosthetic group; this is in contrast with findings elsewhere for urocanase from Pseudomonas putida. Urocanase from Ps. testosteroni does not contain pyridoxal 5'-phosphate as a coenzyme and in this respect is similar to all urocanases studied in purified form.

A structural study of pig liver glyceraldehyde-3-phosphate dehydrogenase

A substantial portion of the primary structure of pig liver glyceraldehyde-3-phosphate dehydrogenase has been investigated and the results compared with those previously reported for the pig muscle enzyme. Liver and muscle glyceraldehyde-3-phosphate dehydrogenases show the same amino acid content, and the first N-terminal residues occur in the same sequence. No differences in N-terminal residues and amino acid composition have been evidenced by analysis of several tryptic peptides, which account for about 50% of the total amino acid sequence. From the electrophoretic mobilities of peptides T8 T9 and T25 it is concluded that residues Asp 60, Asp 67 and Glu 220 in the reported sequence of the pig muscle enzyme must be present as amides in the liver enzyme. The NAD+ content was found to be 2 mol per tetramer, while higher values have been reported for the muscle enzyme from various mammalian sources. The reactivity of lysyl side chains towards pyridoxal 5'-phosphate has been examined: the results indicate that Lys 212 is the main site reacted in fully inactivated pig liver holoenzyme. A similar result has been found for rabbit muscle apoenzyme, whereas rabbit muscle holoenzyme reacts at Lys 212 and 191.

[Modification of the spectrophotometric method of determination of pyridoxal-5'-phosphate and pyridoxal in enzymatic preparations]

In quantitative measurements of pyridoxal-5'-phosphate and pyridoxal in enzymes routinely used phenylhydrasine was substituted for 4-nitrophenylhydrasine. This increased the sensitivity of the method by 70%. The modified procedure had another advantage: it allowed measurements of the optic density of resulting 4-nitrophenylhydrasones at 430 nm for acid solutions and at 550 nm for alkaline solutions.

[Beta-cyanoalanine synthase: Its purification and basic physico-chemical properties]

A method has been developed for the purification of beta-cyano-L-alanine synthase from etiolated 10-day-old seedlings of blue lupine. High purity preparations of the enzyme were obtained with specific activity exceeding 4000-fold that of the seedling homogenate. Preparations were homogeneous on electrophoresis in polyacrylamide gel. The yield of total activity after purification was approximately 20%. Glutamic acid is the enzyme's only N-terminal amino acid; the molecular weight of the enzyme (both native and treated with 6 M urea) is 52000. The synthase containes one mole of pyridoxal-P per mole of protein; its isoelectric point is situated at pH 4,8. The enzyme's absorption spectrum has a maximum at 410 nm i.e., in the characteristic range of many pyridoxal-U-containing enzymes. Data on the amino acid composition of the enzyme are presented.

The conversion of 3-Hydroxy-2,4,5-trihydroxymethylpyridine into pyridoxine by Kloeckera apiculata

Kloeckera apiculata, a vitamin B-6-dependent yeast, grows in the presence of 3-hydroxy-2,4,5-trihydroxymethylpyridine in vitamin B-6-free media. On a molar basis the growth-promoting activity of this compound is approximately one-tenth that of other forms of vitamin B-6. [G-3H]3-Hydroxy-2,4,5-trihydroxymethylpyridine is converted into radioactive vitamin B-6 compounds of the same specific radioactivity by growing cultures of K. apiculata.

Semi-automated system for analysis of vitamin B6 complex by ion-exchange column chromatography

A simple system for semi-automatic analysis of pyridoxal, pyridoxine and pyridoxamine has been developed using diazide of 5-chloroaniline 2,4-disulfonyl chloride as a color-producing reagent in combination with desoxypyridoxine as an internal standard. It employs Aminex A-5 column, 10x0.6ø cm, as an adsorbent. Adsorbates were eluted successively with 3 discrete phosphate buffers (0.4 N Na+). The effluent is mixed continuously with capillary streams of the diazide reagent and of sodium acetate. The mixture, maintained at 65 degrees C in a heating bath, then passes through a spiral of Teflon tubing with a residence time of 2 min. Characteristic orange colored products formed by a diazo coupling reaction are continuously monitored at 440 nm in a flow photometer. The individual peaks on the recorded chromatogram are manually integrated by a conventional HW method. The elution position and recovery of desoxypyridoxine permits correction for sensitivity changes or mechanical losses which might occur during a series of analyses. The analyzer system described allow quantitation from 2 to 25 mug of pyridoxal, pyridoxine and pyridoxamine in a single sample within 2 hr and with a precision of 100 +/- 4%. It is also found suitable as a routine procedure for the analysis of varied biological samples.

Aminotransferase from a deletion mutant in the histidine operon

The imidazolylacetolphosphate:l-glutamate aminotransferase from the deletion mutant hisHB22 has been partially characterized. Although genetic studies have not yet shown the deletion to involve the structural information for this enzyme, physical studies indicate that an abnormal enzyme is produced. Evidence is presented which, together with previous data on the characterization of the enzyme, indicates that the catalytic integrity of the enzyme is intact, and that the low specific activity seen in cell extracts is due to formation of an enzyme which has a reduced coenzyme content. It is suggested that this reduced coenzyme content is due primarily to a reduced affinity of the enzyme (nascent or apo-) for its coenzyme, and that the coenzyme must be incorporated into the enzyme at the moment of synthesis for formation of a functional protein.