Blood-brain exchange routes and distribution of65Zn in rat brain

Zinc is essential for normal development and function of the CNS although much is to be learned about brain Zn homeostasis. In these experiments adult male Wistar rats within the weight range 500–600 g were used. Ventriculo-cisternal perfusion was performed to allow the measurement of⁶⁵Zn fluxes between blood and csf across the choroid plexuses. Blood-brain or blood-cerebrospinal fluid barrier permeability to⁶⁵Zn has been determined by graphical analysis in experiments that lasted between 5 and 180 minutes. Cerebral capillary permeability to⁶⁵Zn was found to be low with a K_in of about 5×10^–4ml/min/g. Choroid plexus permeability to⁶⁵Zn was about 12 fold greater, although Zn influx to brain via this route was <5% that across cerebral capillaries. The autoradiographic distribution of⁶⁵Zn in brain showed regional variation with lowest levels in white matter and high levels in the dentate gyrus and hippocampus.     

DNA sequence changes in mutations induced by ultraviolet light in the gpt gene on the chromosome of Escherichia coli uvr+ and urvA cells

Summary Sequence changes in mutations induced by ultraviolet light are reported for the chromosomal Escherichia coli gpt gene in almost isogenic E. coli uvr ⁺ and excision-deficient uvrA cells. Differences between the mutagenic spectra are ascribed to preferential removal of photoproducts in the transcribed strand by excision repair in uvr ⁺ cells. This conclusion is confirmed by analysis of published results for genes in both uvr ⁺ and uvr ^– cells, showing a similar selective removal of mutagenic products from the transcribed strand of the E. coli lacI gene and of the lambda phage cl repressor gene. Comparison of these data with published results for ultraviolet mutagenesis of gpt on a chromosome in Chinese hamster ovary cells showed that a mutagenic hot spot in mammalian cells is not present in E. coli; the possibility is suggested that the hot spot might arise from localized lack of excision repair. Otherwise, mutagenesis in hamster cells appeared similar to that in E. coli uvr ⁺ cells, except there appears to be a smaller fraction of single-base additions and deletions (frameshifts) in mammalian than in bacterial cells. Phenotypes of 6-thioguanine-resistant E. coli showed there is a gene (or genes) other than gpt involved in the utilization of thioguanine by bacteria.     

Construction and expression of nonsense suppressor tRNAs which function in plant cells

An Arabidopsis thaliana L. DNA containing the tRNA(TrpUGG) gene was isolated and altered to encode the amber suppressor tRNA(TrpUAG) or the ochre suppressor tRNA(TrpUAA). These DNAs were electroporated into carrot protoplasts and tRNA expression was demonstrated by the translational suppression of amber and ochre nonsense mutations in the chloramphenicol acetyltransferase (CAT) reporter gene. DNAs encoding tRNA(TrpUAG) and tRNA(TrpUAA) nonsense suppressor tRNAs caused suppression of their cognate nonsense codons in CAT mRNAs, with the tRNA(TrpUAG) gene exhibiting the greater suppression under optimal conditions for expression of CAT. The development of these translational suppressors which function in plant cells facilitates the study of plant tRNA gene expression and will make possible the manipulation of plant protein structure and function.     

Synthesis and biological activities of angiotensin II and Sarmesin analogues containing cyclohexylalanine

Analogues of angiotensin II with cyclohexylalanine (Cha) at position 4 or 8, and analogues of the competitive (type II) angiotensin antagonist [Sar1,Tyr(Me)4]ANG II (Sarmesin) with Cha at position 8, have been prepared by the solid phase method and purified by reversed-phase HPLC. Analogues of ANG II with Cha at position 8 in which the position 1 residue was substituted with sarcosine (Sar) or amino-isobutyric acid (Aib) or was deleted (Des), were slowly reversing (Type I) antagonists with "pA2" values in the rat isolated uterus assay of approximately 8.5. The additional substitution of Tyr(Me) for Tyr at position 4 of these peptides gave reversible competitive (Type I/II) antagonists with pA2 values of 6.7, 5.8, and less than 5, while substitution of Phe for Tyr gave pA2 values of 7.4, 6.7, and less than 5, respectively. All 19 peptides synthesized in this study had low intrinsic agonist activity in the rat isolated uterus assay except for the type I antagonists [Sar1, Cha8]ANG II (7%), [Aib1, Cha8]ANG II (12%) and [Des1, Cha8]ANG II (20%). These data illustrate that the substitution of Cha at position 8 of ANG II analogues produces potent antagonists; however, Type I antagonists retain significant agonist activity whereas Type I/II antagonists do not. In contrast, substitution of Cha at position 4 in a variety of ANG II analogues resulted in severely diminished biological activity, illustrating that the presence of an aromatic ring quadrupole at position 4 is obligatory for receptor binding and activity.     

Metabolism of 6-nitrochrysene by intestinal microflora.

Since bacterial nitroreduction may play a critical role in the activation of nitropolycyclic aromatic hydrocarbons, we have used batch and semicontinuous culture systems to determine the ability of intestinal microflora to metabolize the carcinogen 6-nitrochrysene (6-NC). 6-NC was metabolized by the intestinal microflora present in the semicontinuous culture system to 6-aminochrysene (6-AC), N-formyl-6-aminochrysene (6-FAC), and 6-nitrosochrysene (6-NOC). These metabolites were isolated and identified by high-performance liquid chromatography, mass spectrometry, and UV-visible spectrophotometry and compared with authentic compounds. Almost all of the 6-NC was metabolized after 10 days. Nitroreduction of 6-NC to 6-AC was rapid; the 6-AC concentration reached a maximum at 48 h. The ratio of the formation of 6-AC to 6-FAC to 6-NOC at 48 h was 93.4:6.3:0.3. Interestingly, compared with results in the semicontinuous culture system, the only metabolite detected in the batch studies was 6-AC. The rate of nitroreduction differed among human, rat, and mouse intestinal microflora, with human intestinal microflora metabolizing 6-NC to the greatest extent. Since 6-AC has been shown to be carcinogenic in mice and since nitroso derivatives of other nitropolycyclic aromatic hydrocarbons are biologically active, our results suggest that the intestinal microflora has the enzymatic capacity to generate genotoxic compounds and may play an important role in the carcinogenicity of 6-NC.     

Microbial metabolism of polycyclic aromatic hydrocarbons: isolation and characterization of a pyrene-degrading bacterium.

Microbiological analyses of sediments located near a point source for petrogenic chemicals resulted in the isolation of a pyrene-mineralizing bacterium. This isolate was identified as a Mycobacterium sp. on the basis of its cellular and colony morphology, gram-positive and strong acid-fast reactions, diagnostic biochemical tests, 66.6% G + C content of the DNA, and high-molecular-weight mycolic acids (C58 to C64). The mycobacterium mineralized pyrene when grown in a mineral salts medium supplemented with nutrients but was unable to utilize pyrene as a sole source of carbon and energy. The mycobacterium grew well at 24 and 30 degrees C and minimally at 35 degrees C. No growth was observed at 5 or 42 degrees C. The mycobacterium grew well at salt concentrations up to 4%. Pyrene-induced Mycobacterium cultures mineralized 5% of the pyrene after 6 h and reached a maximum of 48% mineralization within 72 h. Treatment of induced and noninduced cultures with chloramphenicol showed that pyrene-degrading enzymes were inducible in this Mycobacterium sp. This bacterium could also mineralize other polycyclic aromatic hydrocarbons and alkyl- and nitro-substituted polycyclic aromatic hydrocarbons including naphthalene, phenanthrene, fluoranthene, 3-methylcholanthrene, 1-nitropyrene, and 6-nitrochrysene. This is the first report of a bacterium able to extensively mineralize pyrene and other polycyclic aromatic hydrocarbons containing four aromatic rings.     

The effect of testosterone on citrate synthesis and citrate oxidation and a proposed mechanism for regulation of net citrate production in prostate

Citrate oxidation by rat ventral prostate was reduced by castration and increased by testosterone administration. Similarly, the mitochondrial aconitase activity was decreased by castration; whereas cytosol aconitase was unaffected. The rate of citrate oxidation is extremely low in prostate. Castration also decreased mitochondrial aspartate aminotransferase activity while having no effect on the cytosol isoenzyme. Testosterone markedly stimulated the net production of citrate from aspartate plus glutamate by prostate mitochondria. These studies support the proposal that aspartate is a major source of oxalacetate for citrate production, and that a "glutamate-aspartate-citrate" pathway may be functional in prostate mitochondria. In addition, testosterone can regulate citrate production by a specific effect on mitochondrial aspartate aminotransferase activity. Testosterone also regulates the flux of citrate through the Krebs cycle, but this represents only a small proportion of the citrate accumulated. These conditions would be consistent with the function of prostate epithelium in accumulating and secreting citrate.     

Calcium-dependent anion channel in the water mold,Blastocladiella emersonii

Summary Injection of depolarizing current into vegetative cells of the water moldBlastocladiella emersonii elicits a regenerative response that has the electrical characteristics of an action potential. Once they have been taken past a threshold of about –40 mV, cells abruptly depolarize to +20 mV or above; after an interval ranging from several hundred milliseconds to a few seconds, the cells spontaneously return to their resting potential near –100 mV. When the action potential was analyzed with voltage-clamp recording, it proved to be biphasic. The initial phase reflects an influx of calcium ions through voltage-sensitive channels that also carry Sr²⁺ ions. The delayed, and more extended, phase of inward current results from the efflux of chloride and other anions. The anion channels are broadly selective, passing chloride, nitrate, phosphate, acetate, succinate and even PIPES. The anion channels open in response to the entry of calcium ions, but do not recognize Sr²⁺. Calcium channels, anion channels and calcium-specific receptors that link the two channels appear to form an ensemble whose physiological function is not known. Action potentials rarely occur spontaneously but can be elicited by osmotic downshock, suggesting that the ion channels may be involved in the regulation of turgor.     

Evidence that 1-naphthol is not an obligate intermediate in the covalent binding and the pulmonary bronchiolar necrosis by naphthalene

Recent studies of a number of volatile aromatic hydrocarbons have suggested that the formation of covalently bound metabolites arises solely through the intermediate formation of phenols. This study further examines the involvement of 1-naphthol in the in vivo and in vitro formation of covalently bound metabolites and pulmonary bronchiolar necrosis by naphthalene. Marked differences were observed in the rate of 1-naphthol formation in lung and liver microsomal incubations without correspondingly large differences between the rates of formation of covalently bound metabolites from naphthalene and 1-naphthol. Glutathione decreased covalent binding in hepatic microsomal incubations containing 14[C]1-naphthol but did not result in the formation of any of the glutathione adducts isolated from identical incubations containing 14[C]naphthalene. Tissue levels of covalently bound radioactivity in mice treated with 14[C]1-naphthol or 14[C]naphthalene were similar; however, in contrast to studies with naphthalene, 1-naphthol administration did not deplete tissue glutathione nor result in detectable tissue injury. These studies indicate that 1-naphthol is not an obligate intermediate in the formation of covalently bound metabolites from naphthalene nor does it appear to be a more proximate lung toxic metabolite.