Studies on biologically active pteridines. III. The absolute configuration at the C-6 chiral center of tetrahydrobiopterin cofactor and related compounds

Tetrahydrobiopterin, the natural pteridine cofactor for aromatic amino acid hydroxylases, was produced stereopecifically with reference to the C-6 chiral center from 7,8-dihydrobiopterin by the action of dihydrofolate reductase. Similarly, 7,8-dihydro-6-methylpterin was reduced to tetrahydro-6-methylpterin having the same 6-configuration by the same enzyme. The absolute configuration of these tetrahydropterins at the C-6 chiral center was determined to be L, as in (2S)-1,2,3,4-tetrahydro-2-methylquinoxaline, which was servied from L-alanine, by comparison of the CD spectra.

Effects of structures of tetrahydropterin cofactors on rat brain tryptophan hydroxylase

Effects of structures of the side chain at position 6 of 12 tetrahydropterin cofactors including 4 stereoisomers of tetrahydrobiopterin and tetrahydroneopterin on the activity of rat brain tryptophan hydroxylase were examined. Tetrahydrobiopterins and tetrahydroeneopterins having a side chain of a L-erythro or or D-threo configuration showed lower Km values for both the pterin cofactor and tryptophan substrate and also higher V values than their enantiomers. L-erythro-Tetrahydrobiopterin had the highest cofactor activity among all the pterin cofactors examined. Since reduction of biopterin to tetrahydrobiopterin introduces another center of asymmetry at 6-position of the pterin ring, L-erythro-tetrahydrobiopterin obtained by chemical reduction is a mixture of two diastereoisomers. The two diastereoisomers of L-erythro--tetrahydrobiopterin, i.e. (6R)-L-erythro-tetrahydropterin and the (6S)-isomer were separated by high-performance liquid chromatography, and were examined for their cofactor activity. The two diastereoisomers gave similar Km values toward pterin itself and toward tryptophan, but the natural (6R)-isomer gave much higher V values than the (6S)-isomer; the (6S)-isomer was nearly inactive for rat brain tryptophan hydroxylase because of its very low V value. These results support the hypothesis that (6R)-L-erythro-tetrahydrobiopterin may be the natural cofactor of rat brain tryptophan hydroxylase.

Isolation of octapeptin D (studies on antibiotics from the genus Bacillus. XXVII)

A new peptide antibiotic complex, named octapeptin D, was isolated from culture broth of a microorganism belonging to the genus Bacillus. The trihydrochloride of the antibiotic was obtained as a colorless powder, soluble in water and methanol. The empirical formula, C47H88N12O11.3HCl.H2O, was indicated by elemental analysis. Amino acid analysis on the acid hydrolyzate demonstrated the presence of 2,4-diaminobutyric acid (4 moles), serine (1 mole) and leucine (3 moles). Gas chromatographic analysis with the methylated product of the ethereal extract of the acid hydrolyzate revealed the presence of beta-hydroxy isodecanoic acid, beta-hydroxy decanoic acid, beta-hydroxy isoundecanoic acid and beta-hydroxyanteisoundecanoic acid. Octapeptin D is active against Gram-negative and Gram-positive bacteria in vitro and in vivo.

Conformation of ribonuclease S-protein

Ribonuclease S-protein exhibits a pH-dependent conformational transition between folded and unfolded states, and some unfolded S-protein persists up to pH 8. The histidine C2 proton resonance of the unfolded species was erroneously assigned by Bradbury et al. to histidine residue 119 of the folded species.

Characterization of the Bacillus subtilis motile system driven by an artificially created proton motive force

Transient swimming was induced in energy-depleted cells of Bacillus subtilis by an artificial proton motive force, which was created by valinomycin addition and a pH reduction. This system did not require any ions except protons in the medium. The size of the induced motility was strongly influenced by changes in the size of either the K+ diffusion potential or the pH gradient. A rough estimation indicated that a proton motive force higher than -100 mV was required for induction of translational swimming of the cell. Corresponding with the transient appearance of swimming, a rapid but transient efflux of K+ and influx of H+ were observed. With decreases in the rate of H+ influx, the amount of motility decreased. A rate of H+ influx higher than 0.2 mumol/s per ml of cell water gave translational swimming. These results suggest direct coupling of H+ influx to rotation of bacterial flagella.

Immunoelectron-microscopic studies of endoplasmic reticulum-Golgi relationships in the intracellular transport process of lipoprotein particles in rat hepatocytes

Endoplasmic reticulum (ER)-Golgi relationships in the intracellular transport process of secretory proteins in rat hepatocytes have been studied using lipoprotein particles as a marker for the secretory protein and cytochrome P-450 as a marker enzyme for the ER membranes. Ferritin immunoelectron-microscopic observation revealed that, while almost all the microsomal vesicles derived from ER membranes are heavily labelled with ferritin anti-cytochrome P-450 antibody conjugates, labelling of the small peripheral vesicles containing lipoprotein particles, the stacks of Golgi saccules, especially the outermost saccule which is sometimes fenestrated, condensing vacuoles in the trans-Golgi region and the secretion droplets of lipoprotein were scanty and at the control level. Such a characteristic pattern of labelling was especially evident when these structures were prepared from phenobarbital-treated rats. These findings indicate that the membranes of the small peripheral vesicles do not contain cytochrome P-450 and that the cytochrome is probably not transferred to Golgi saccules in the transport process of lipoprotein from ER to Golgi. It is suggested, therefore, that the small peripheral vesicles are formed by budding of the special regions of ER membrane where microsomal marker proteins such as cytochrome P-450 are excluded and the membrane proteins destined to the Golgi complexes are clustered. It is also shown that lysosomal membranes are not labelled with the anti P-450 antibody conjugates.

Induction of hepatic tumors in rats by senkirkine and symphytine

The carcinogenicity of the pyrrolizidine alkaloids senkirkine and symphytine was studied in male inbred ACI rats. Animals were divided into 3 groups: Group I received ip injections of freshly prepared senkirkine at a dose of 10% of the median lethal dose (LD50) twice weekly for 4 weeks and then once a week for 52 weeks. Group II received ip injections of symphytine at a dose of 10% of the LD50 by the same injection schedule as in group I. The control group was given ip injections of a 0.9% NaCl solution following the same injection schedule as in experimental groups. All group I rats survived for more than 290 days after the start of injections, and 9 of 20 rats developed liver cell adenoma. All group II animals survived for more than 330 days after the start of injections. Of 20 rats, 4 had liver tumors, 3 had hemangioendothelial sarcomas, and 1 had liver cell adenoma. The hemangioendothelial sarcomas showed metastasis in the lungs of 2 rats. The control group had no liver tumors.

Quantitative immunoelectron-microscopic analyses of the distribution of cytochrome P-450 molecules on rat liver microsomes

Specific antibodies to phenobarbital-induced cytochrome P-450 were prepared by affinity chromatography and coupled to ferritin with glutaraldehyde. The ferritin antibody conjugates with molecular ratio of approximately one were isolated by gel filtration and were used for immunochemical and immunoelectron-microscopic analyses of the distribution of cytochrome P-450 on microsomes from untreated, phenobarbital- and methylcholanthrene-treated rats. Binding assay showed that at the saturation level of the antibodies, microsomes from untreated, phenobarbital- and methylcholanthrene-treated rats bind 0.25, 0.41 and 0.14 mol of the antibody per mol of cytochrome P-450, respectively. From these data, the maximum number of the ferritin particles which can bind with microsomes was calculated. This number was in good agreement with the average number of ferritin particles bound per microsome which was determined by electron-microscopic observations of the microsomes incubated with the antibody conjugates at saturation level. Electron-micriscopic observations also indicated that smooth microsomes can bind more conjugates than rough microsomes and this finding was consistent with the biochemical data that, on the protein basis, smooth microsomes comtain more cytochrome P-450 than rough microsomes, even after correction for ribosomal proteins. The number of ferritin particles bound per smooth microsome was proportional to the diameter and non-random distribution of the ferritin particles on the microsomal vesicles, which was deduced simply by inspection in the previous paper from this laboratory, was confirmed by statistical analyses of electron micrographs of the labelled microsomes.

A human chorionic gonadotropin-specific antiserum against synthetic peptide analogs to the carboxyl-terminal peptide of its beta-subunit

A chemically synthesized Na-acetyl-triacontapeptide analogous to the carboxyl-terminal region (residues 116--145) of hCG beta-subunit was conjugated to bovine thyroglobulin. This synthetic antigen was used to immunize five rabbits; one of these rabbits (H-114) generated a useable antiserum. The binding properties of this antiserum were compared extensively to a well characterized antiserum (H-93) against the natural tricosaglycopeptide (residues 123--145) of desialylated hCG beta-subunit conjugated to bovine serum albumin. The two antisera showed nearly identical immunological specificities and sensitivities when examined in a conventional RIA system. These similarities included: 1) antibody recognition sites residing at the carboxyl-terminal pentadecapeptide region; 2) binding neither [125I]iodo-hLH nor [125I]iodo-oLH; and 3) lack of neutralizing capability against the biological activity of hCG in vivo. However, synthetic pentadeca or longer peptides are twice as potent in inhibiting 125I]iodo-hCG binding to H-114 than to H-93. Synthetic peptides may provide a superior means of generating antisera capable of distinguishing hCG from human LH, since they can be obtained more easily in large quantities than analogous purified natural fragments and because peptides of synthetic origin avoid the risk of contamination from strongly antigenic regions of the native molecules. Such hCG-specific antisera may have extensive application in RIA systems and fertility control, where selective binding to hCG but not human LH is desired.

Effects of kanamycin on the auditory evoked responses during postnatal development of the hearing of the rat

The ototoxic effects of kanamycin were studied in rats during the early postnatal period and at an adult age. Brain stem potentials as well as auditory cortical potentials were used for the estimating of ototoxic damage. The auditory potentials decreased promptly and markedly in the animals which were treated daily with 400 mg/kg body weight of kanamycin starting from the 11th day after birth. In these animals, the auditory potentials were almost completely abolished within 10 days after the beginning of the kanamycin treatment. However, when the same amount of kanamycin was applied earlier or later than that, i.e., avoiding the period of the initial appearance and the greatest development of auditory functions (from the 11th to the 15th day after birth in the rat), the auditory potentials were not apparently damaged. In light and scanning electronmicroscopy, marked ototoxic changes were observed which underlay the functional damage. The meaning of these findings is discussed.

Immunoelectron microscope localization of cytochrome P-450 on microsomes and other membrane structures of rat hepatocytes

Localization of cytochrome P-450 on various membrane fractions of rat liver cells was studied by direct immunoelectron microscopy using ferritin-conjugated antibody to the cytochrome. The outer surfaces of almost all the microsomal vesicles were labeled with ferritin particles. The distribution of the particles on each microsomal vesicle was usually heterogeneous, indicating clustering of the cytochrome, and phenobarbital treatment markedly increased the labeled regions of the microsomal membranes. The outer nuclear envelopes were also labeled with ferritin particles, while on the surface of other membrane structures such as Golgi complexes, outer mitochondrial membranes and plasma membranes the labeling was scanty and at the control level. The present observation indicates that cytochrome P-450 molecules are localized exclusively on endoplasmic reticulum membranes and outer nuclear envelopes where they are probably distributed not uniformly but heterogeneously, forming clusters or patches. The physiological significance of such microheterogeneity in the distribution of the cytochrome on endoplasmic reticulum membranes is discussed.

Isolation of tridecaptins A, B and C (studies on antibiotics from the genus Bacillus. XXIII)

Three new antibiotics, tridecaptins A, B and C, were isolated from culture broths of strains of Bacillus polymyxa AR-110, B-2 and E-23, respectively. All are acyl tridecapeptides differing from each other in the fatty acid components and amino acid residues. They are weakly active against Gram-negative and Gram-positive bacteria in vitro and in vivo.

Adaptive rundown of excitatory post-synaptic potentials at synapses between hair cells and eight nerve fibres in the goldfish

1. The excitatory post-synaptic potentials (e.p.s.p.s.) evoked by sound stimuli were recorded intracellularly from large afferent eight nerve fibres in the sacculus of the goldfish (S1 fibres). The fish were anaesthetized with MS-222 and spike potentials were suppressed with locally applied tetrodotoxin. 2. The e.p.s.p.s. successively evoked in response to each wound wave showed a marked rundown in size, while no reduction was observed in the microphonic potentials. The amplitude of successive e.p.s.p.s was reduced keeping approximately a fixed ratio to the preceding ones, suggesting that the rundown is attributable to a depletion of transmitter quanta from the release sites. 3. The rate of rundown of successive e.p.s.p.s, however, remained almost unchanged when the intensity of the stimulus sound was changed. It was also observed that, even after the e.p.s.p.s had been completely adapted to a continuous sound, a vigorous discharge of new e.p.s.p.s was observed when the intensity of the sound was increased. 4. These findings seem to indicate that it is the size of the readily available store and not the release fraction that is changed by a change in the sound intensity. 5. The saccular macula was superfused with solutions different in Ca and Mg ion concentrations. High Ca ion concentration brought about an increase in the size of the readily available store as well as the release fraction. 6. Mechanisms underlying these observations were discussed in terms of the quantal release mechanism as well as the morphology of the release sites.

Quantal analysis of the size of excitatory post-synaptic potentials at synapses between hair cells and afferent nerve fibres in goldfish

1. A statistical analysis has been made of the transmitter release at the hair cell afferent fibre synapse in the sacculus of the goldfish, using the amplitude of the excitatory post-synaptic potentials (e.p.s.p.s) in response to stimulus tone as a measure of the transmitter release under application of tetrodotoxin. 2. Application of binomial statistics allowed a direct calculation of the mean probability of release (p) and the readily available store (n), and the X2-test showed that the binomial predictions fitted fairly well with the observed distribution of the responses. 3. Adaptive rundown of e.p.s.p.s during sound stimulation, i.e. the successive rundown in the size of the mean quantal content (m), was found to be associated with a reduction in the size of parameter n, but not of p. 4. A marked negative correlation was demonstrated between the amplitude of two consecutive e.p.s.p.s, supporting the depletion hypothesis of the adaptive rundown of e.p.s.p.s. 5. The increase in the e.p.s.p. amplitude and the increase in the mean quantal content, m, brought about by an increase in the tone intensity were found mostly explicable in terms of an increase in the statistical parameter n. The probability parameter p was found largely in invariable, although in certain instances the increase in m was also accompanied by a slight increase in the parameter p.

Catabolic conversion of sepiapterin to 6-(1-carboxyethoxy)pterin by Bacillus subtilis

Structural elucidation of an intensely blue fluorescent compound (A) formed from sepiapterin by Bacillus subtilis is described. The structure of the catabolite (A) was found to be 2-amino-6-(1-carboxyethoxy)-4(3H)-pteridinone (9) from both spectroscopic and degradation studies. This was confirmed by an unambiguous synthesis of 9. The stereochemical structure of the side chain at the 6-position of A was confirmed to be the L(or S) configuration, as in sepiapterin, by analysis of the lactic acid formed from A on acid hydrolysis. This suggests that the side chain is rearranged intact during the catabolic conversion of sepiapterin. A possible mechanism for the conversion is discussed.