Diffusive and convective transport through hollow fiber membranes for liver cell culture

For an efficient membrane bioreactor design, transport phenomena determining the overall mass flux of metabolites, catabolites, cell regulatory factors, and immune-related soluble factors, need to be clarified both experimentally and theoretically. In this work, experiments and calculations aimed at discerning the simultaneous influence of both diffusive and convective mechanisms to the transport of metabolites. In particular, the transmembrane mass flux of glucose, bovine serum albumin (BSA), APO-transferrin, immunoglobulin G, and ammonia was experimentally measured, under pressure and concentration gradients, through high-flux microporous hydrophilic poly-ether-sulphone (PES-HFMs) and poly-sulphone hollow fiber membranes (PS-HFMs). These data were analyzed by means of a model based on the mechanism of capillary pore diffusion, assuming that solute spherical molecules pass through an array of solvent-filled cylindrical pores with a diffusive permeation corrected for friction and steric hindrances. Additionally, resistances to the mass transfer were taken into account. Convective permeation data were discussed in terms of morphological properties of the polymeric membranes, molecular Stokes radius, and solute-membrane interactions according to information given by contact angle measurements. The observed steady-state hydraulic permeance of PS-HFMs was 0.972 L/m2hmbar, about 15.6-fold lower than that measured for PES-HFMs (15.2 L/m2h); in general, PS-HFMs provided a significant hindrance to the transport of target species. Diffusion coefficients of metabolites were found to be similar to the corresponding values in water through PES-HFMs, but significantly reduced through PS-HFMs (D(Glucose)(Membrane)=2.8x10(-6)+/-0.6x10(-6)cm2/s, D(BSA)(Membrane)=6.4 x 10(-7)+/-1 x 10(-7)cm(/s, D(Apotransferrin)(Membrane)=2.3 x 10(-7)+/-0.25 x 10(-7)cm2/s).

Role of metal ions on the secondary and quaternary structure of alkaline phosphatase from bovine intestinal mucosa

Alkaline phosphatase (EC 3.1.3.1) from bovine intestinal mucosa (BIAP) is an homodimeric metalloenzyme, containing one Mg2+ and two Zn2+ ions in each active site. ApoBIAP, prepared using ion-chelating agents, exhibited a dramatic decrease of its hydrolase activity, concomittant to conformational changes in its quaternary structure. By rate-zonal centrifugation and electrophoresis, we demonstrated, for the first time, that the loss of divalent ions leads to some monomerization process for a metal-depleted alkaline phosphatase. Divalent ions are also involved in the secondary and tertiary structures. Metal-depletion induced more exposure of some Trp residues and hydrophobic regions to the solvent (as proved by intrinsic and ANS fluorescences). These changes might correspond to the disappearance of alpha-helices and/or turns with a concomittant appearance of unordered structures and beta-sheets (as probed by FTIR spectroscopy). For BIAP, three steps of temperature-induced changes were exhibited, while for apoBIAP, only one step was exhibited at 55 degrees C. Our work on BIAP showed two main differences with alkaline phosphatase from Escherichia coli. The loss of the divalent ions induces protein monomerization and the total recovery of enzyme activity by divalent ion addition to apoBIAP was not obtained.

Comparison of the backbone dynamics of the apo- and holo-carboxy-terminal domain of the biotin carboxyl carrier subunit of Escherichia coli acetyl-CoA carboxylase

The biotin carboxyl carrier protein (BCCP) is a subunit of acetyl-CoA carboxylase, a biotin-dependent enzyme that catalyzes the first committed step of fatty acid biosynthesis. In its functional cycle, this protein engages in heterologous protein-protein interactions with three distinct partners, depending on its state of post-translational modification. Apo-BCCP interacts specifically with the biotin holoenzyme synthetase, BirA, which results in the post-translational attachment of biotin to a single lysine residue on BCCP. Holo-BCCP then interacts with the biotin carboxylase subunit of acetyl-CoA carboxylase, which leads to the addition of the carboxylate group of bicarbonate to biotin. Finally, the carboxy-biotinylated form of BCCP interacts with transcarboxylase in the transfer of the carboxylate to acetyl-CoA to form malonyl-CoA. The determinants of protein-protein interaction specificity in this system are unknown. The NMR solution structure of the unbiotinylated form of an 87 residue C-terminal domain fragment (residue 70-156) of BCCP (holoBCCP87) and the crystal structure of the biotinylated form of a C-terminal fragment (residue 77-156) of BCCP from Escherichia coli acetyl-CoA carboxylase have previously been determined. Comparative analysis of these structures provided evidence for small, localized conformational changes in the biotin-binding region upon biotinylation of the protein. These structural changes may be important for regulating specific protein-protein interactions. Since the dynamic properties of proteins are correlated with local structural environments, we have determined the relaxation parameters of the backbone 15N nuclear spins of holoBCCP87, and compared these with the data obtained for the apo protein. The results indicate that upon biotinylation, the inherent mobility of the biotin-binding region and the protruding thumb, with which the biotin group interacts in the holo protein, are significantly reduced.

The pH of the host niche controls gene expression in and virulence of Candida albicans

Little is known of the biological attributes conferring pathogenicity on the opportunistic fungal pathogen Candida albicans. Infection by this pathogen, as for bacterial pathogens, may rely upon environmental signals within the host niche to regulate the expression of virulence determinants. To determine if C. albicans responds to the pH of the host niche, we tested the virulence of strains with mutations in either of two pH-regulated genes, PHR1 and PHR2. In vitro, PHR1 is expressed when the ambient pH is at 5.5 or higher and deletion of the gene results in growth and morphological defects at neutral to alkaline pHs. Conversely, PHR2 is expressed at an ambient pH below 5.5, and the growth and morphology of the null mutant is compromised below this pH. A PHR1 null mutant was avirulent in a mouse model of systemic infection but uncompromised in its ability to cause vaginal infection in rats. Since systemic pH is near neutrality and vaginal pH is around 4.5, the virulence phenotype paralleled the pH dependence of the in vitro phenotypes. The virulence phenotype of a PHR2 null mutant was the inverse. The mutant was virulent in a systemic-infection model but avirulent in a vaginal-infection model. Heterozygous mutants exhibited partial reductions in their pathogenic potential, suggesting a gene dosage effect. Unexpectedly, deletion of PHR2 did not prevent hyphal development in vaginal tissue, suggesting that it is not essential for hyphal development in this host niche. The results suggest that the pH of the infection site regulates the expression of genes essential to survival within that niche. This implies that the study of environmentally regulated genes may provide a rationale for understanding the pathobiology of C. albicans.

Defects in assembly of the extracellular matrix are responsible for altered morphogenesis of a Candida albicans phr1 mutant

Analysis of Candida albicans cells using antibodies directed against Gas1p/Ggp1p, Saccharomyces cerevisiae homolog of Phr1p, revealed that Phr1p is a glycoprotein of about 88 kDa whose accumulation increases with the rise of external pH. This polypeptide is present both in the yeast form and during germ tube induction. In the Phr1- cells at pH 8 the solubility of glucans in alkali is greatly affected. In the parental strain the alkali-soluble/-insoluble glucan ratio shows a 50% decrease at pH 8 with respect to pH 4.5, whereas in the null mutant it is unchanged, indicating the lack of a polymer cross-linker activity induced by the rise of pH. The mutant has a sixfold increase in chitin level and is hypersensitive to calcofluor. Consistently with a role of chitin in strengthening the cell wall, Phr1- cells are more sensitive to nikkomycin Z than the parental strain.

PHR2 of Candida albicans encodes a functional homolog of the pH-regulated gene PHR1 with an inverted pattern of pH-dependent expression

Deletion of PHR1, a pH-regulated gene of Candida albicans, results in pH-conditional defects in growth, morphogenesis, and virulence evident at neutral to alkaline pH but absent at acidic pH. Consequently, we searched for a functional homolog of PHR1 active at low pH. This resulted in the isolation of a second pH-regulated gene, designated PHR2. The expression of PHR2 was inversely related to that of PHR1, being repressed at pH values above 6 and progressively induced at more acidic pH values. The predicted amino acid sequence of the PHR2 protein, Phr2p, was 54% identical to that of Phr1p. A PHR2 null mutant exhibited pH-conditional defects in growth and morphogenesis analogous to those of PHR1 mutants but manifest at acid rather than alkaline pH values. Engineered expression of PHR1 at acid pH in a PHR2 mutant strain and PHR2 at alkaline pH in a PHR1 mutant strain complemented the defects in the opposing mutant. Deletion of both PHR1 and PHR2 resulted in a strain with pH-independent, constitutive growth and morphological defects. These results indicate that PHR1 and PHR2 represent a novel pH-balanced system of functional homologs required for C. albicans to adapt to environments of diverse pH.

Effect of carrageenan-induced granuloma on hepatic cytochrome P-450 isozymes in rats

Carrageenan-induced granuloma was used to study the apoprotein and RNA content, and catalytic activities of several cytochrome P-450 isozymes in liver. This model allowed discrimination between acute and chronic phases of experimental inflammation. The expression of most isozymes studied (CYP2D, CYP2E1, CYP3A1 and CYP4A) was reduced to 20% of the control level during the acute phase and partially recovered (30-60% of control group) during the chronic phase. CYP2B1 content was decreased to 65% of control during the acute and chronic phases of inflammation. RNA (CYP2B1 and CYP2E1) showed a strong depression during the acute phase and recovered during the chronic phase, without differences between isoenzymes. In most cases, there was a good correlation between the apoprotein content of isozymes and related activities. Our results show that the depletion of cytochrome P-450 induced by inflammation depends on the severity of the disease. Experimental inflammation equally affect the transcription of CYP2B1 and CYP2E1, so differences in apoprotein content and related activities between isozymes may due to differential posttranscriptional regulation.

Capillary electrophoretic analysis of serine hydroxymethyltransferase in Escherichia coli fermentation broth

Serine hydroxymethyltransferase (SHMT) expressed in Escherichia coli was analyzed in fermentation broth through the use of capillary electrophoresis (CE), a method which provided advantages over the traditional techniques of slab gel electrophoresis and chromatography. In addition, via CE the difficult resolution and quantitation of SHMT holoenzyme and apoenzyme were achieved. Using this method, a pyridoxal-5'-phosphate (PLP) cofactor/SHMT dimer molar ratio of 0.65 was estimated to be present in holoenzyme in the absence of excess PLP. This determination correlated well with results obtained by other techniques, including electrospray ionization mass spectrometry (ESI-MS). CE and ESI-MS analyses both provided evidence for significant differences between the folded conformations of SHMT holoenzyme and apoenzyme.

Salivary theophylline monitoring: reassessment and clinical considerations

To assess the reliability of salivary theophylline concentrations for patient monitoring, concentrations of theophylline in sera and saliva of 50 patients (ages 6-81 years) receiving oral or parenteral theophylline were determined by two methods: a rapid dry-phase apoenzyme reactivation system (ARIS) and fluorescence polarization immunoassay (FPIA). Saliva production was stimulated by both citric acid (CA) and parafilm (PF). With both analytical methods, there were excellent correlations between salivary theophylline concentration, CS, and unbound serum theophylline concentration CU (r2 > 0.95), and between CS and total serum theophylline concentration, CT (r2 > 0.85). CA- and PF-stimulated CS by FPIA resulted in concentrations within 2.0 micrograms/ml of the actual CU for 100% of the samples measured (n = 47). By ARIS, 100% of the PF-stimulated CS and 93.6% of the CA-stimulated CS determinations were within 2.0 micrograms/ml of the CU (n = 47). To evaluate the predictive capabilities of PF- and CA-stimulated saliva, one-half (n = 24) of the patients were randomly selected and their data used to predict the CT for the remaining patients. FPIA PF-CS predicted 83.3% (20/24) of CT within +/- 2 micrograms/ml, while ARIS CA-CS predicted 75.0% within +/- 2 micrograms/ml. There was no difference between FPIA CS and ARIS CS results by multivariate analysis of variance (MANOVA), but there was a difference between PF-CS and CA-CS (p < 0.05). However, when CU was used as a covariant, there was no significant difference. Using appropriate saliva collection procedures and the FPIA system, we conclude that CS provides adequate reliability for therapeutic drug monitoring of theophylline.

The nifY product of Klebsiella pneumoniae is associated with apodinitrogenase and dissociates upon activation with the iron-molybdenum cofactor

Apodinitrogenase, which lacks the iron-molybdenum cofactor at its active site, is an oligomer that contains an additional protein not found in the active dinitrogenase tetramer. This associated protein in Klebsiella pneumoniae is shown to be the product of the nifY gene. When apodinitrogenase is activated by the addition of the iron-molybdenum cofactor, NifY dissociates from the apodinitrogenase complex. The conditions for this dissociation are described. Finally, there are aspects of the dissociation and insertion process in K. pneumoniae that are different from that in Azotobacter vinelandii.

Evaluation of the holoenzyme content of aromatic L-amino acid decarboxylase in brain and liver tissues

We have re-evaluated the content of the holo-form of aromatic L-amino acid decarboxylase in rat tissues. Aromatic L-amino acid decarboxylase was found to consume pyridoxal 5'-phosphate while it underwent decarboxylation-dependent transamination as a side reaction. We observed that the total dopamine formation was proportional to the amount of holoenzyme. Dopamine formation in a tissue extract, which was preincubated with pyridoxal 5'-phosphate, was compared with the same tissue sample but which was prepared without preincubation. Percentages of holo-form of aromatic L-amino acid decarboxylase obtained from such comparison were 78% for brain and 94% for liver tissues. These values were significantly higher than those reported earlier in which the decarboxylation-dependent transamination of the decarboxylase had been overlooked.

Regulatory properties of brain glutamate decarboxylase (GAD): the apoenzyme of GAD is present principally as the smaller of two molecular forms of GAD in brain

The apoenzyme of glutamate decarboxylase [enzyme without bound cofactor, pyridoxal 5'-phosphate (pyridoxal-P)] serves as a reservoir of inactive glutamate decarboxylase (GAD) that can be activated when additional GABA synthesis is required. We have investigated which of two molecular forms of GAD is present as apoenzyme in synaptosomes and in cortex, caudate nucleus, hippocampus, and cerebellum of rat brain. Endogenous glutamate apodecarboxylase (apoGAD) was labeled by incubating extracts of synaptosomes or punches of each region with 32P-pyridoxal-P, followed by reduction with NaBH4, to link covalently the 32P-pyridoxal-P to GAD. Proteins were separated by SDS-PAGE. Punches from all four brain regions and forebrain synaptosomes contained two forms of GAD with apparent Mrs of 63 and 65 kDa as identified by immunoblotting with four antiGAD sera. Punches and synaptosomes contained a major 32P-pyridoxal-P-labeled band with an apparent Mr of 63 kDa that was stained on immunoblots by the antiGAD serum 1440 and the monoclonal antibody GAD-6, and a minor labeled band at 65 kDa that was stained by the 1440, 6799, and K2 antisera. Synaptosomes contained remarkably few other strongly labeled proteins, but punches contained several other labeled bands. Three additional lines of evidence indicate that the labeled 63-kDa protein is apoGAD: (1) it was purified by immunoaffinity chromatography with the GAD-1 monoclonal antibody; (2) it yielded one major labeled peptide when digested with chymotrypsin, and that peptide appeared identical in peptide-mapping experiments to the labeled active-site peptide isolated from chromatographically prepared rat brain GAD; and (3) its labeling was selectively blocked by 4-deoxypyridoxine 5'-phosphate, a competitive inhibitor of the binding of pyridoxal-P to GAD.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of tyrosine hydroxylase apoenzyme protein by enzyme-linked immunosorbent assay (ELISA): effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on striatal tyrosine hydroxylase activity and content

A enzyme-linked immunosorbent assay has been developed for tyrosine hydroxylase (TH). The method uses a polyclonal antibody to trap TH, a monoclonal antibody to bind the immobilized TH, a biotinylated, anti-mouse immunoglobulin to bind the monoclonal antibody, and streptavidin covalently coupled to horseradish peroxidase (SA-HRP). The antigen-antibody complex is detected colorometrically following incubation with an HRP substrate. The method detects less than 1 ng (16 fmol) of TH and can be performed in 3 h. The high specificity of the assay is attributed to the use of both polyclonal and monoclonal antibodies, each of which are specific for TH. Data acquisition and reduction is rapid and linked directly to a common desktop computer. Levels of TH protein average 1 ng/microgram protein in striatum and, following treatment with the neurotoxicant MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), are decreased to a similar extent as is catalytic activity. In contrast, MPTP did not alter TH homospecific activity. The monoamine oxidase B inhibitor deprenyl blocked both the decrease in activity and the decrease in immunoreactive protein caused by MPTP.

19th Sir Hans Krebs lecture. Engineering of protein bound iron-sulfur clusters. A tool for the study of protein and cluster chemistry and mechanism of iron-sulfur enzymes

An increasing number of iron-sulfur (Fe-S) proteins are found in which the Fe-S cluster is not involved in net electron transfer, as it is in the majority of Fe-S proteins. Most of the former are (de)hydratases, of which the most extensively studied is aconitase. Approaches are described and discussed by which the Fe-S cluster of this enzyme could be brought into states of different structure, ligation, oxidation and isotope composition. The species, so obtained, provided the basis for spectroscopic and chemical investigations. Results from studies by protein chemistry, EPR, Mössbauer, 1H, 2H and 57Fe electron-nuclear double resonance spectroscopy are described. Conclusions, which bear on the electronic structure of the Fe-S cluster, enzyme-substrate interaction and the enzymatic mechanism, were derived from a synopsis of the recent work described here and of previous contributions from several laboratories. These conclusions are discussed and summarized in a final section.

Purification and properties of carnitine dehydratase from Escherichia coli--a new enzyme of carnitine metabolization

Carnitine dehydratase from Escherichia coli 044 K74 is an inducible enzyme detectable in cells grown anaerobically in the presence of L(-)-carnitine or crotonobetaine. It has been purified 500-fold to electrophoretic homogeneity by chromatography on phenyl-Sepharose, hydroxyapatite, DEAE-Sepharose, second phenyl-Sepharose and finally gel filtration on a Sephadex G-100 column. During the purification procedure a low-molecular-weight effector essential for enzyme activity was separated from the enzyme. The addition of this still unknown effector caused reactivation of the apoenzyme. The relative molecular mass of the apoenzyme has been estimated to be 85,000. It seems to be composed of two identical subunits with a relative molecular mass of 45,000. The purified and reactivated enzyme has been further characterized with respect to pH and temperature optimum (7.8 and 37-42 degrees C), equilibrium constant (Keq = 1.5 +/- 0.2) and substrate specifity. The enzyme is inhibited by thiol reagents. The Km value for crotonobetaine is 1.2.10(-2) M. gamma-Butyrobetaine, D(+)-carnitine and choline are competitive inhibitors of crotonobetaine hydration.

Reactions of phosphonate analogs of pyridoxal phosphate with apo-aspartate aminotransferase

We have investigated reactions of the 5-phosphonoethyl and 5-phosphonoethenyl analogs of pyridoxal 5'-phosphate in the coenzyme site of cytosolic aspartate aminotransferase. Acid dissociation constants and equilibrium constants for hydration and for tautomerization have been evaluated for these compounds. In confirmation of previous results, both compounds are partially active. They bind to apoenzyme well and undergo conversion in the presence of glutamate to amine forms which show induced circular dichroism comparable to that of native enzyme. A normal "external" Schiff base is evidently formed with 2-methylaspartate, but the amounts of quinonoid intermediate formed with erythro-3-hydroxyaspartate are less than those formed with pyridoxal phosphate. The pKa of the imine group of the enzyme reconstituted with the phosphonoethyl analog is more than two units lower than that in the native enzyme. Binding of the dicarboxylates glutarate, 2-oxoglutarate, and succinate shifts the pKa upward. The absorption spectra of the resulting complexes indicate the existence of at least three low pH species. A shift of 2.3 to 2.9 ppm to a lower frequency was observed for the 31P NMR signal upon binding of these dicarboxylates or of 2-methylaspartate. Enzyme containing the analogs crystallizes. Polarized absorption spectra suggest that the coenzyme has an orientation similar to that of pyridoxal phosphate in the native enzyme.

Zinc metabolism in Ehrlich cells: properties of a metallothionein-like zinc-binding protein

Host zinc deficiency halts the proliferation of the mouse Ehrlich ascites tumor. The major site of measurable cellular zinc depletion is a cytosolic zinc binding protein. This protein is characterized as a metallothionein on the basis of its presence as two isoproteins which behave on DEAE-Sephadex and in polyacrylamide gel electrophoresis like metallothioneins, the lack of protein absorbance at 280 nm, its sulfhydryl/zinc ratio of 3.5, and its reactivity in zinc transfer to apocarbonic anhydrase. Finally, the protein exhibits cross-reactivity with a known rat metallothionein in a radioimmunoassay. Coupled with the similarity in structure and antigenicity of rat and mouse metallothioneins, this adds strong support to the identification of the zinc-binding protein as a metallothionein. In zinc-deficient cells this metallothionein-like protein appears to exist as an apoprotein. When small amounts of dietary zinc stimulate the deficient cells to divide, zinc is not observed in metallothionein. Larger concentrations of dietary zinc support both proliferation and the steady state presence of zinc in this protein. It is demonstrated that metallothionein is the principal donor of zinc to apocarbonic anhydrase added to Ehrlich cytosol. These results are used to construct a model of zinc metabolism in which zinc metallothionein is a labile depot of zinc in the Ehrlich cell which can be mobilized under zinc-deficient conditions.

Dry reagent immunoassay for measuring phenobarbital in serum and plasma

A reagent strip has been developed for measuring phenobarbital concentrations in serum or plasma. This strip utilizes the apoenzyme reactivation immunoassay system (ARIS) and is designed for use with the Ames Seralyzer reflectance photometer. The test takes 85 s and compares strip reactivities with a two-point calibration line that is stored in the instrument. Within-run precision coefficient of variation ranges from 2.4 to 4.1% over five concentrations while the between-run precision ranges from 2.3 to 4.9%. Results obtained with clinical serum samples correlated well (r greater than 0.99) with those obtained by a fluorescence polarization immunoassay (TDx). The strips crossreact with other barbituric acid derivatives that are not coadministered with phenobarbital. Crossreactivity to the metabolite p-hydroxyphenobarbital is sufficiently low as to not interfere in the usual specimens. Samples that are hemolyzed, highly icteric, or from uremic patients should be avoided. This assay is a rapid and convenient method for monitoring serum or plasma phenobarbital concentrations. It is particularly well suited for decentralized test sites, such as emergency rooms, urgent care centers, and physician's offices.

Comparison of rat and mouse ornithine aminotransferase with respect to molecular properties and regulation of synthesis

A comparative study of the synthesis patterns and molecular properties of mouse and rat ornithine aminotransferase (OAT) was conducted. The two enzymes were found to be very similar with respect to catalytic properties, two-dimensional electrophoresis patterns of tryptic digests, amino acid compositions, and antibody cross-reactivity. In vitro translation assays for OAT synthesis on free polysomes isolated from livers at different times of day showed similar circadian fluctuations in OAT synthesis for both species. However, hybridization measurements revealed no circadian changes in the levels of hybridizable OAT mRNA in these livers. These results demonstrate that the circadian cycling of OAT synthesis is regulated at the level of translation in both the rat and the mouse.

Quantitative description of absorption spectra of a pyridoxal phosphate-dependent enzyme using lognormal distribution curves

Ultraviolet-visible absorption spectra of cytosolic aspartate aminotransferase of pig hearts have been analyzed by resolution with lognormal distribution curves. These have been compared with spectra of reference Schiff bases of pyridoxal 5'-phosphate. Spectra of the free enzyme in two different states of protonation and of complexes with monoanions, dicarboxylates, the substrates L-glutamate, L-aspartate, and L-erythro-3-hydroxyaspartate, and the quasi-substrate 2-methylaspartate have been analyzed. Relative amounts of three tautomeric species have been estimated, as have amounts of various enzyme-substrate intermediates. Bandshape parameters which can be used as a guide to analysis of spectra of other pyridoxal phosphate-dependent enzymes are tabulated. Some formation constants and pKa values, which were evaluated at the same time as the spectra of the complexes, are also reported.

[Detection of ligand-induced conformation changes in lactate dehydrogenase by using fluorescent probes]

The binding of ANS to apolactate dehydrogenase (apo-LDH) is accompanied by a 300-fold increase in dye fluorescence with a shift of the emission maximum from 515 to 479 nm, as well as by quenching of intrinsic protein fluorescence. A tetrameric LDH molecule has 6.4 +/- 1.6 non-interacting dye-binding sites with an association constant equal to (4.3 +/- 1.6) X 10(3) M-1. NAD+ added at saturating concentrations does not alter the number of ANS binding sites or the association constant value. The formation of binary LDH.NAD+, LDH.NADH, LDH.AMP and LDH.pyruvate complexes causes the quenching of fluorescence of the enzyme-bound ANS. The extent of quenching observed at ligand saturating concentrations differs for each ligand. Pyruvate added to the binary LDH.AMP complex exerts no effect on the fluorescence of protein-bound ANS; this indicates that the binding of AMP causes some alterations in the microenvironment of the substrate-binding site. Nicotinamide mononucleotide (NMN) can act as a coenzyme in the LDH-catalyzed reaction. AMP added together with NMN displays an inhibitory effect. The cationic (auramine O) and anionic (ANS) fluorescent probes bound to LDH exhibit different responses to conformational changes accompanying the transition from the apoenzyme to the LDH X NAD-pyruvate complex.

Regional distribution in rat brain of tryptophan hydroxylase apoenzyme determined by enzyme-linked immunoassay

Tryptophan hydroxylase apoenzyme was measured in 21 regions of the rat brain by a competitive enzyme-linked immunoassay (ELISA) technique using a recently developed antiserum from the sheep to this protein. Highest apoenzyme levels were found in the pineal gland and in the dorsal raphé. An insignificant level was observed in the cerebellum. In general, the distribution of tryptophan hydroxylase apoenzyme follows the distribution of serotonin previously detected by immunocytochemistry. A turnover number for tryptophan hydroxylase in a rat brain supernatant fraction of 7.5 s-1 was estimated, a value far higher than that estimated for serotonin turnover in vivo. This result confirms that serotonin biosynthesis is additionally regulated by factors other than tryptophan hydroxylase apoenzyme concentration.

Kinetic aspects of the role of phospholipids in D-beta-hydroxybutyrate dehydrogenase activity

Interactions of phospholipids with D-beta-hydroxybutyrate dehydrogenase (BDH), a lecithin-requiring enzyme, have been studied by a kinetic approach. The process of reactivation of BDH by phospholipids, which follows a second-order mechanism, reveals that (1) at least 2 mol of lecithins is essential for the reactivation of the enzyme, and (2) the enzyme contains two dependent binding sites for lecithins. The graphic representation of the time course of reactivation shows a latent phase which decreases when there is an increase in the amount of phospholipids. A Scatchard plot treatment of the reactivation kinetic data reveals the presence of two classes of phospholipid binding sites, which exhibit high and low affinities related to the binding of four and two lecithin molecules, respectively. The effect of temperature on BDH activity and on the inactivation of the apoenzyme with N,N'-dicyclohexylcarbodiimide (a specific carboxyl reagent) or with phenylglyoxal (a specific arginine reagent) shows a break at 22-24 degrees C, indicating a slight structural change in the enzyme-active site around this temperature. In addition, the variations in enzyme kinetic parameters, according to the nature of phospholipids, are in agreement with conformational changes related to the nature and to the fluidity state of phospholipids. However, the apparent NAD+ binding constant does not depend on the phospholipid's fluidity.

Nuclear magnetic resonance studies of the old yellow enzyme. 2. 13C NMR of the enzyme recombined with 13C-labeled flavin mononucleotides

The apoenzyme of NADPH oxidoreductase, 'old yellow enzyme', was reconstituted with selectively 13C-enriched flavin mononucleotides and investigated by 13C NMR spectroscopy. The 13C NMR results confirm the results obtained by 15N NMR spectroscopy and yield additional information about the coenzyme-apoenzyme interaction. A strong deshielding of the C(2) and C(4) atoms of enzyme-bound FMN both in the oxidized and reduced state is observed, which is supposed to be induced by hydrogen-bond formation between the protein and the two carbonyl groups at C(2) and C(4) of the isoalloxazine ring system. The chemical shifts of all 13C resonances of the flavin in the two-electron-reduced state indicate that the N(5) atom is sp3-hybridized. From 31P NMR measurements it is concluded that the FMN phosphate group is not accessible to bulk solvent. The unusual 31P chemical shift of FMN in old yellow enzyme seems to indicate a different binding mode of the FMN phosphate group in this enzyme as compared to the flavodoxins. The 13C and 15N NMR data on the old-yellow-enzyme--phenolate complexes show that the atoms of the phenolate are more deshielded whereas the atoms of the enzyme-bound isoalloxazine ring are more shielded upon complexation. A non-linear correlation exists between the chemical shifts of the N(5) and the N(10) atoms and the pKa value of the phenolate derivative bound to the protein. Since the chemical shifts of N(5), N(10) and C(4a) are influenced most on complexation it is suggested that the phenolate is bound near the pyrazine ring of the isoalloxazine system. 15N NMR studies on the complex between FMN and 2-aminobenzoic acid indicate that the structure of this complex differs from that of the old-yellow-enzyme--phenolate complexes.

Nuclear magnetic resonance studies of the old yellow enzyme. 1. 15N NMR of the enzyme recombined with 15N-labeled flavin mononucleotides

The apoenzyme of NADPH oxidoreductase, 'old yellow enzyme', was reconstituted with specifically 15N-labeled flavin mononucleotide and investigated by 15N NMR spectroscopy in the oxidized and reduced state. The results indicate that in the oxidized state a hydrogen bond is formed between the N(5) atom and the apoprotein. In addition, hydrogen bonds exist between the N(1) and N(3) atoms of FMN and the apoprotein. The resonance position of N(10) indicates that this atom is somewhat sp3-hybridized, i.e. lifted out of the molecular plane of the isoalloxazine ring system. In the reduced state the N(1) atom is negatively charged and the N(3) atom forms a hydrogen bond with the apoprotein. The N(10) atom in protein-bound FMN exhibits about the same hybridization state as in free anionic reduced FMN, i.e. it is located in the plane of the isoalloxazine ring. The chemical shift of the N(5) resonance indicates that this atom is almost completely sp3-hybridized. This interpretation can also be derived from the 15N(5)-1H coupling constant. Among the flavoproteins thus far studied by NMR techniques, old yellow enzyme is the only protein that shows a conformation of the reduced prosthetic group with the N(5) atom lifted out of the molecular plane. The isoelectric focussing properties of old yellow enzyme and a new easy method for the preparation of the apoprotein are also reported.

Isolation and characterization of an enkephalin-hydrolyzing dipeptidyl-aminopeptidase from calf-brain striatum

Cytosolic dipeptidyl-aminopeptidase with a high affinity for Leu-enkephalin (Km = 5-7 microM) was partially purified from the 25,000 g supernatant of calf-brain striatum. The procedure included pH 4.5 denaturation, DEAE-cellulose chromatography and Blue Sepharose CL-6B chromatography and resulted in preparations that are free from other enkephalin-hydrolyzing enzymes. This enzyme, which is called enkephalinase B, has a positively charged group in its active site and presumably also a Zn atom since the loss in activity induced by EDTA treatment can be restored without loss of substrate affinity by low concentrations of ZnSO4.

Site-specific immobilization of flavin adenine dinucleotide on indium/tin oxide electrodes through flavin adenine amino group

A Mannich-type reaction was used to attach flavin adenine dinucleotide (FAD) covalently to aminosilane derivatized indium/tin oxide-coated glass plates. The aminosilane was activated with formaldehyde to give an intermediate that attached specifically to the adenine amino group of FAD. The presence of the intermediate also was demonstrated by coupling hydroquinone to the formaldehyde activated support. The immobilized FAD and hydroquinone were characterized by cyclic or differential pulse voltammetry. The immobilized FAD was shown to reduce the overpotential for NADH oxidation by 180 mV. In keeping with results for FAD on glassy carbon, FAD attached to indium/tin oxide at the adenine amino group did not lead to reconstitution of activity with apoglucose oxidase.

Effect of phosphate and other inorganic anions on the activity of chicken liver cytosolic aspartate aminotransferase

Chicken liver aspartate aminotransferase was inhibited by several inorganic anions. The inhibitory effect of the anions was related to their chaotropic character. Apparent Km (2-oxoglutarate) and Km (L-aspartate) values depended on the molarity of the buffer. The profile of the curves obtained did not depend on the nature of the enzyme sample assayed. Phosphate slightly inhibited the holoaspartate aminotransferase and was a strong inhibitor of apoaspartate aminotransferase with respect to pyridoxal phosphate.

[Cytosol aspartate aminotransferase from the chicken heart: three-dimensional structure at 2.8 angstroms resolution and the characteristic conformation of various enzyme forms]

The spatial structure of cytosolic chicken aspartate aminotransferase (AAT) has been determined by X-ray crystallographic analysis at 2.8 A resolution. AAT consists of two chemically identical subunits. Each subunit can be subdivided into the large pyridoxal phosphate (PLP) binding domain and the small domain. The two active sites of AAT are situated in deep clefts at the subunit interface. The binding of PLP and 2-oxoglutarate is described. Conformations of the following enzyme forms have been compared by difference Fourier syntheses: the nonliganded PLP-form in phosphate and acetate buffers; the non-liganded pyridoxamine phosphate (PMP) form; complexes of the PLP-form with glutarate and 2-oxoglutarate. Lattice-induced dynamic asymmetry of the dimeric AAT molecules was revealed. In one subunit the small domain is mobile and shifted either toward the active site ("closed" conformation) or in the opposite direction ("open" conformation). The closed conformation is induced by the binding of dicarboxylate anions. In the second subunit the small domain is immobile and shifted toward the active site in all enzyme forms or complexes studied. In this subunit, there occurs a rotation of the PLP ring by approximately 20 degrees toward the substrate site. The rotation is observed when crystals are soaked in 0.6 saturated (NH4)2SO4 solution buffered with 0.3 M potassium phosphate, pH 7.5; it was explained by formation of an external aldimine between PLP and NH3. This aldimine is not formed in the presence of dicarboxylates or acetate. It was inferred that dicarboxylate or acetate anions stabilize the internal PLP-lysine aldimine and prevent its reaction with ammonia. Conversion of AAT from the PLP- to PMP-form is accompanied by rotation of the coenzyme ring by approximately 20 degrees; the rotation occurs in both subunits.

[Purification of homogeneous gamma-cystathionase and study of its structure by circular dichroism]

Rat liver gamma-cystathionase has been purified to homogeneity (verified by SDS electrophoresis and ultracentrifugation). The secondary and tertiary structures of the enzyme were studied by circular dichroism spectra. Our studies revealed that the holoenzyme molecule comprises approximately 22% of alpha-helices, 14% of beta-structure, 14% of beta-bends, and 50% of unordered structure. Conformational alterations of the enzyme molecule resulting from enzyme PLP elimination, reduction with sodium borohydride and irreversible inhibition by propargylglycine were examined. The enzyme's secondary structure was shown to be stable whereas the tertiary structure is labile. Saturation with PLP maintains the enzyme's optimal (catalytically active) tridimensional structure. Sodium dodecylsulfate alters its secondary (the amount of alpha-helix being raised to 34%) and tertiary structures.

Benign methylmalonic aciduria

Methylmalonic aciduria due to methylmalonyl-CoA mutase deficiency is usually considered to be a serious, often life-threatening disease. However, through routine screening of urine in neonates or screening of siblings of clinically affected neonates, we have identified eight children who have a benign clinical variant of this disorder. Their urinary methylmalonic acid levels have ranged from 1.0 to 3.4 mg per milligram of creatinine, with serum values ranging from an undetectable level to 1.7 mg per deciliter (130 nmol per liter). The children have not received dietary or vitamin therapy, have had normal growth and development (age range, 18 months to 13 years), and have performed as well as their unaffected siblings on psychometric testing. These children have no evidence of a deficiency of vitamin B12, which acts as a cofactor with methylmalonyl-CoA mutase, and they did not respond to the administration of vitamin B12. Two siblings were found by complementation analysis to have a defect in the methylmalonyl-CoA mutase apoenzyme; complementation analysis was not performed on the other patients. We conclude that the clinical spectrum of methylmalonyl-CoA mutase deficiency is wider than indicated by previously reported cases.

[Luminescent properties of NADPH: adrenodoxin reductase]

The fluorescent and phosphorescent properties of NADPH-adrenodoxin reductase were investigated. It was shown that the fluorescence of protein tryptophanyls was quenched completely by acrylamide and partially by ionic quenchers (I- and Cs+). A removal of the prosthetic group from the protein causes insignificant changes in fluorescent properties of the enzyme. The denaturation of the enzyme by urea was accompanied by growth of quenching parameters. Indeed, some differences were observed in the quenching of flavin fluorescence by ionic quenchers (I- and Cs+). NADPH appeared to be an efficient quencher of NADPH-adrenodoxin reductase tryptophan fluorescence. Using Förster's equations for non-radiative energy transfer, the distance between NADPH-binding site and tryptophanyls was evaluated to 35-40 A.

Age-related effects of nutritional vitamin B6 deficiency on B6-dependent enzymes of glutamate, gamma-aminobutyrate and glutamine systems in the rat brain

Effect of nutritional vitamin B6 deficiency on the activities of enzymes-glutamic acid decarboxylase (GAD), gamma aminobutyric acid transaminase (GABA-T), aspartate amino-transferase (AsAT), alanine aminotransferase (AlAT) and glutamotransferase (GT) was studied in the rat brain of different age groups. Deficiency was induced at one day (group 1), 21 days (group 2), three months (group 3), 12 months (group 4) and 24 months (group 5) for a period of 3-10 weeks. When the holo and apoenzyme levels were compared in control and B6 deficient rats, it was found that GAD, GABA-T, AsAT and AlAT holoenzyme levels were significantly lower in the deficient rats of all the five groups whereas the level of GT holoenzyme was low only in group 1, the other groups did not show any significant change. GAD apoenzyme level was significantly higher in the deficient animals of group 1 and 2 while the reverse was true for GABA-T apoenzyme and no significant variation was seen in the older groups. It is interesting to note that the level of AsAT apoenzyme was significantly low in older age groups (4, 5) as a function of B6 deficiency, while AlAT and GT apoenzymes were not affected in any age group studied.

[Isolation and characterization of glycerol dehydrogenase from bacillus megaterium]

Glycerol dehydrogenase of high purity was isolated from Bacillus megaterium. The enzyme has a pH optimum of 9 and dehydrogenizes in presence of NAD+ glycerol as well as 1,2-propanediol and, to a smaller extent, erythritol. The Michaelis constant for glycerol is 1.4 X 10(-3)M and for NAD+ 3 X 10(-4)M. With the application of different methods (density gradient centrifugation, gel electrophoresis and gel chromatography) relative molecular masses of 156 000-160 000 were ascertained. In the dodecyl sulfate electrophoresis we found a molecular mass of 38 000 per subunit, so that the native enzyme is existent in the tetrameric form. By means of fluorescence titration one NADH binding site per subunit could be estimated. The amino-acid composition was determined. The enzyme is stable only in the presence of high thiol concentrations. Heavy metal ions and chelating agents inhibit the activity of the enzyme. Zinc, presumably, is the natural heavy metal in the active center, but other divalent metal ions can also activate the apoenzyme. With the help of chemical modification reactions, the probable presence of one essential thiol group and one essential tyrosine residue per subunit could be demonstrated.

The iron content of iron superoxide dismutase: determination by anomalous scattering

The number of iron atoms in the dimeric iron-containing superoxide dismutase from Pseudomonas ovalis and their atomic positions have been determined directly from anomalous scattering measurements on crystals of the native enzyme. To resolve the long-standing question of the total amount of iron per molecule for this class of dismutase, the occupancy of each site was refined against the measured Bijvoet differences. The enzyme is a symmetrical dimer with one iron site in each subunit. The iron position is 9 A from the intersubunit interface. The total iron content of the dimer is 1.2 +/- 0.2 moles per mole of protein. This is divided between the subunits in the ratio 0.65:0.55; the difference between them is probably not significant. Since each subunit contains, on average, slightly more than half an iron atom we conclude that the normal state of this enzyme is two iron atoms per dimer but that some of the metal is lost during purification of the protein. Although the crystals are obviously a mixture of holo- and apo-enzymes, the 2.9 A electron density map is uniformly clean, even at the iron site. We conclude that the three-dimensional structures of the iron-bound enzyme and the apo-enzyme are identical.

Thermodynamic characterization of hog kidney D-amino acid oxidase apoenzyme in concentrated guanidine hydrochloride solution. Preferential interaction with the solvent components and the molecular weight of the monomeric unit

This paper describes the physical characterization of the monomeric unit of hog kidney D-amino acid oxidase apoenzyme in 6 M guanidine hydrochloride (GuHCl) solution by means of differential refractometry, densimetry, light scattering, equilibrium sedimentation, and high-speed gel filtration chromatography. In 6 M GuHCl solution, the oxidase interacts preferentially with GuHCl: the values of the preferential interaction parameter are 0.11 +/- 0.03 (S.D.) g/g of protein by densimetry and 0.14 +/- 0.04 g/g of protein by refractometry. The volume change, delta V, of the oxidase on transfer from the native to the denatured state is -350 ml/mol. The molecular weight of the monomeric apoenzyme is 39,600 +/- 1,700 by light scattering and 38,000 +/- 1,200 by high-speed equilibrium sedimentation. The values of the molecular weight estimated by the empirical methods, i.e., sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis and high-speed gel filtration chromatography in 6 M GuHCl, agree well with those obtained by the thermodynamic methods mentioned above. These results confirm definitely that the complex of the apoenzyme with SDS normally behaves in the same manner as those of standard proteins in SDS-gel electrophoresis. This is also supported in this study by the analysis of the electrophoretic data at several gel concentrations by Ferguson plots. The molecular weight of quasi-D-amino acid oxidase apoenzyme was also examined by the empirical methods.

1H n.m.r. of the DNA-dependent RNA polymerase from Escherichia coli

The (1)H n.m.r. study of the DNA-dependent RNA polymerase from Escherichia coli has revealed that the holoenzyme (betabeta'alpha(2)sigma) displays two mobile regions: one, observable also in the core enzyme (betabeta'alpha(2)), is characterized by basic amino acids and its appearance and form depend on ionic strength; the other, specific to the holoenzyme, is characterized by threonine residues and its appearance does not depend on ionic strength.

Subunit localizations of zinc(II) in DNA-dependent RNA polymerase from Escherichia coli B

RNA Polymerase holoenzyme and core enzyme from Escherichia coli B have been shown to contain two zinc ions. Flameless atomic absorption spectroscopy of the isolated core subunits indicated that one zinc ion is localized on the beta subunit and the other is bound on the beta' subunit. Atomic fluorescence spectroscopy showed that prolonged dialysis of the metalloenzyme against 0.01 M o-phenanthroline resulted in the removal of both zinc(II) ions with accompanying loss of enzymatic activity. The activity of the apoenzyme was observed to be completely restored by readdition of zinc(II) and partially restored by cobalt(II).

Enzymatic dtermination of pyridoxal 5'-phosphate with gamma-cyanoaminobutyric acid aposynthase

A rapid alternative method is presented for the determination of pyridoxal 5'-phosphate (pyridoxal-P). The method involves the colorimetric analysis of thiocyanate liberated from S-cyanohomocysteine (Hcy (CN)) in the presence of cyanide when catalyzed by the pyridoxal-P dependent enzyme, gamma-cyano-alpha-aminobutyric acid (gamma-CNabu)-synthase (Hcy (CN) thiocyano-lyase [adding CN]). The rate of formation of thiocyanate is determined by the increase in absorbance at 470 nm on treatment of the enzymatic reaction mixture with FeCl3.

The determination of thiamin pyrophosphate in blood and other tissues, and its correlation with erythrocyte transketolase activity

A sensitive method for the specific measurement of thiamin pyrophosphate (TPP) has been developed using the apoenzyme recombination concept. Yeast pyruvic decarboxylase apoenzyme can be reconstituted by the addition of TPP or samples containing TPP, yielding the holoenzyme with activity proportionate to the amount of TPP added. Using this technique, reaction mixtures containing 0.2 to 1.5 ng TPP can be assayed. Normal human erythrocyte TPP ranges from 50 to 150 ng per ml packed cells. When rats are fed a thiamin deficient diet, the erythrocyte TPP level falls more rapidly than the erythrocyte transketolase activity. After 8 days, the level of TPP in the erythrocytes of deficient animals was 10% of the level in pair-fed controls. At this time, however, there was no appreciable decrease in their respective transketolase activities. The level of TPP in the liver also is decreased drastically after 8 days. Therefore it appears that erytyrocyte and liver TPP stores have begun to be depleted and suggest that erythrocyte TPP levels are a more sensitive indicator of thiamin status.

Critical residues in D-amino acid oxidase. A pulse-radiolysis and inactivation study

The enzyme D-amino acid oxidase and its apoenzyme have been irradiated at pH 5.5--10 under conditions designed to assess the inactivating effect of OH radicals and the selective free radicals Br2- and (SCN)2-. Near neutral pH, removal of the coenzyme FAD from the enzyme results in greater inactivation by selective free-radical attack. From pulse-radiolysis spectra, this increase is associated with attack on tyrosine and tryptophan residues in the protein. A large increase in inactivation of both the haloenzyme and apoenzyme by selective free-radical attack is seen with increasing alkalinity. This is consistent with attack on tyrosine being of major importance.

Concerning the metalloenzyme ascorbate oxidase

Apoascorbate oxidase has been shown to have a molecular weight of 137,000 +/- 3,000 and essentially the same gross quaternary conformation as native ascorbate oxidase. The apoenzyme, however, lacks much of the conformational stability of the native enzyme. The removal of the copper from the oxidase protein, and the simultaneous reduction of the disulfide bonds results in an apoenzyme of lower structural stability than the native oxidase. The aging of apoascorbate oxidase has been found to involve a loss of ionizable tyrosine residues and a dissociation to subunits and component polypeptide chains, which was not observed with the more stable native and holo enzymes. The molecular weight of holoascorbate oxidase has been determined to be 285,000. An s020, w of 9.79 has been determined for the holoenzyme. Holoascorbate oxidase has been shown to have an electrophoretic mobility on polyacrylamide gels that is 23% lower than either the native or apoenzyme. Furthermore, electrophoresis of the holoenzyme, in buffers containing dodecyl sulfate, and also isoelectric focusing of the holenzyme, produce patterns of greater similarity to those of apoascorbate oxidase than the native enzyme.

Purification of the cyclooxygenase that forms prostaglandins. Demonstration of two forms of iron in the holoenzyme

The fatty acid cyclooxygenase (ec 1.14.99.1) that produces the prostaglandin and thromboxane precursor, 15-hydroperoxy-9 alpha, 11 alpha-peroxidoprosta-5, 13-dienoic acid (PGG2), has been purified from sheep vesicular glands to a specific activity of 46,000 units/mg of protein by combining detergent solubilization, (NH4)SO4 fractionation, chromatography on DEAE-cellulose and Flurbiprofen-Sepharose, isoelectric focusing, and gel filtration. The final enzyme preparation exhibited only one band of 70,000 molecular weight following sodium dodecyl sulfate gel electrophoresis and staining with Coomassie blue. Treatment of the purified oxygenase with [3H] acetylsalicylic acid yielded a radioactive product which co-electrophoresed with the protein of 70,000 molecular weight. Thus, the isolated protein appeared to be the same one which, in crude preparations, selectively binds acetyl groups in association with prostaglandin synthetic activity. Incubation of the purified oxygenase with [1-14C] arachidonic acid in the presence of stannous chloride yielded only 9 alpha, 11 alpha, 15-trihydroxy-prosta-5,13-dienoic acid (PGF2alpha). Without stannous chloride, a mixture of radioactive products was observed which was characteristic of nonenzymic breakdown of PGG2. Thus, the isolated enzyme catalyzed the insertion of both oxygen molecules required for the formation of prostaglandins and thromboxanes from polyunsaturated fatty acid substrates. The aerobic absorption spectrum of the isolated oxygenase showed a faint peak at 412 nm indicative of heme. The iron content indicated that a significant amount of nonheme iron was present. The purified oxygenase was activated by added hemin, which was readily bound to the protein. The subsequently isolated heme-protein complex showed a major absorption peak at 407 nm.

Animal liver tryptophan pyrrolases: Absence of apoenzyme and of hormonal induction mechanism from species sensitive to tryptophan toxicity

1. Liver tryptophan pyrrolase exists as holoenzyme and apoenzyme in rat, mouse, pig, turkey, chicken and possibly man. 2. The apoenzyme is absent from cat, frog, gerbil, guinea pig, hamster, ox, sheep and rabbit. 3. The hormonal mechanism of induction of the pyrrolase is absent from species lacking the apoenzyme. 4. The concentrations of tryptophan in livers and sera of these species are lower than in species possessing the apoenzyme. 5. Species lacking the apoenzyme or the hormonal induction mechanism have a deficient kynurenine pathway and are sensitive to the toxicity of tryptophan. 6. It is suggested that these species are not suitable as models for studying human tryptophan metabolism. 7. The possible significance of these findings in relation to veterinary and human neonatal care is discussed.

[Purification and certain properties of pyruvate decarboxylase from bovine brain]

A procedure of isolation and purification of pyruvate decarboxylase (PDC) from bovine brain is worked out. 350-fold purified enzyme preparation was homogenous under polyacrylamide gel electrophoresis. Molecular weight of PDC from bovine brain was estimated to be 180 000 by means of gel chromatography through Sephadex G-200. The protein was eluted in two peaks (with molecular weight of 180 000 and 90 000 respectively). After the treatment of the enzyme preparation with 6 M guanidine chloride. Probably, partial dissociation of the enzyme molecule into two subunits takes place in this case. Data on paper chromatography confirmed that highly purified PDC preparations from bovine brain were isolated as apoenzyme, since they were almost free of TPP.