Is a Schiff base involved in the mechanism of the delta4-3-oxo steroid 5alpha- or 5beta-reductases from mammalian liver?
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ABSTRACT:
SUBMITTER: Wilton DC
PROVIDER: S-EPMC1172870 | biostudies-other | 1976 Jun
REPOSITORIES: biostudies-other
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Project description:[2-18O]Ribulose 5-phosphate was prepared and shown to be converted enzymically by 6-phosphogluconate dehydrogenase from sheep liver into 6-phosphogluconate with complete retention of the heavy isotope. This finding unequivocally excludes the possibility of a Schiff-base mechanism for the enzyme. The involvement of metal ions has already been excluded, and other possible mechanisms are discussed. The enzyme was purified by an improved large-scale procedure, which is briefly described.
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Project description:The regulatory mechanisms involved in the control of the nuclear NADPH-dependent 3-ketosteroid 5alpha-reductase (5alpha-reductase) activity were studied in liver, kidney and prostate. The substrate used was [1,2-(3)H]androst-4-ene-3,17-dione (androstenedione) (for liver and kidney) or [4-(14)C]androstenedione (for prostate). The hepatic nuclear 5alpha-reductase activity was greater in female than in male rats, was greater in adult than in prepubertal female rats, increased after castration of male rats, but was not affected by treatment with testosterone propionate or oestradiol benzoate. These regulatory characteristics are in part different from those previously described for the hepatic microsomal 5alpha-reductase. The renal nuclear metabolism of androstenedione, i.e. 5alpha reduction and 17beta-hydroxy steroid reduction, was relatively unaffected by sex, age, castration and treatment with testosterone propionate. However, treatment of castrated male rats with oestradiol benzoate led to a significant increase in the 5alpha-reductase activity and a significant decrease in the 17beta-hydroxy steroid reductase activity. Finally, the nuclear 5alpha-reductase activity in prostate was androgen-dependent, decreasing after castration and increasing after treatment with testosterone propionate. In conclusion, the nuclear 5alpha-reductase activities in liver, kidney and prostate seem to be under the control of distinctly different regulatory mechanisms. The hypothesis is presented that whereas the prostatic nuclear 5alpha-reductase participates in the formation of a physiologically active androgen, 5alpha-dihydrotestosterone, this may not be the true function of the nuclear 5alpha-reductase in liver and kidney. These enzymes might rather serve to protect the androgen target sites in the chromatin from active androgens (e.g. testosterone) by transforming them into less active androgens (e.g. 5alpha-androstane-3,17-dione and/or 5alpha-dihydrotestosterone).
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Project description:Steroid hormones synchronize a variety of functions throughout all stages of life. Importantly, steroid hormone-transforming enzymes are ultimately responsible for the regulation of these potent signaling molecules. Germline mutations that cause dysfunction in these enzymes cause a variety of endocrine disorders. Mutations in SRD5A2, HSD17B3, and HSD3B2 genes that lead to disordered sexual development, salt wasting, and other severe disorders provide a glimpse of the impacts of mutations in steroid hormone transforming enzymes. In a departure from these established examples, this review examines disease-associated germline coding mutations in steroid-transforming members of the human aldo-keto reductase (AKR) superfamily. We consider two main categories of missense mutations: those resulting from nonsynonymous single nucleotide polymorphisms (nsSNPs) and cases resulting from familial inherited base pair substitutions. We found mutations in human AKR1C genes that disrupt androgen metabolism, which can affect male sexual development and exacerbate prostate cancer and polycystic ovary syndrome (PCOS). Others may be disease causal in the AKR1D1 gene that is responsible for bile acid deficiency. However, given the extensive roles of AKRs in steroid metabolism, we predict that with expanding publicly available data and analysis tools, there is still much to be uncovered regarding germline AKR mutations in disease.
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Project description:In this study, bifurfural, an inedible biobased chemical and a second-generation biomass, was polymerized with several diamines using an environmentally benign process, and the chemical structures of the resulting poly(Schiff base)s were analyzed. Because furan rings, which are only produced from biomass and not from fossil resources, endow polymers with unique properties that include high rigidity and expanded π-conjugation, bifurfural, which contains two furan rings, is of significant interest as a biobased building block. 1H NMR, IR, and matrix assisted laser desorption ionization-time of flight mass spectra of the poly(Schiff base)s reveal that they are composed of mixtures of linear and cyclic structures. The UV-vis spectroscopy and molecular orbital theory confirm the extended π-conjugation in the bifurfural/p-phenylenediamine poly(Schiff base) system. Poly(Schiff base)s composed of bifurfural and 1,3-propanediamine, 1,4-butandiamine, 1,5-pentanediamine, and 1,6-hexanediamine were molded at 120 °C into films that exhibited good strengths and were tough to bend. These results indicate that bifurfural-based poly(Schiff base)s are promising biobased materials.
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Project description:In this work we analyze the whole molecular mechanism for intramolecular aromatic hydroxylation through O2 activation by a Schiff hexaazamacrocyclic dicopper(I) complex, [Cu(I) 2(bsH2m)](2+). Assisted by DFT calculations, we unravel the reaction pathway for the overall intramolecular aromatic hydroxylation, i.e., from the initial O2 reaction with the dicopper(I) species to first form a Cu(I)Cu(II)-superoxo species, the subsequent reaction with the second Cu(I) center to form a μ-η(2):η(2)-peroxo-Cu(II) 2 intermediate, the concerted peroxide O-O bond cleavage and C-O bond formation, followed finally by a proton transfer to an alpha aromatic carbon that immediately yields the product [Cu(II) 2(bsH2m-O)(μ-OH)](2+).
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Project description:The retinal protonated Schiff-base (RPSB) in its all-trans form is found in bacterial rhodopsins, whereas visual rhodopsin proteins host 11-cis RPSB. In both cases, photoexcitation initiates fast isomerization of the retinal chromophore, leading to proton transport, storage of chemical energy or signaling. It is an unsolved problem, to which degree this is due to protein interactions or intrinsic RPSB quantum properties. Here, we report on time-resolved action-spectroscopy studies, which show, that upon photoexcitation, cis isomers of RPSB have an almost barrierless fast 400 fs decay, whereas all-trans isomers exhibit a barrier-controlled slow 3 ps decay. Moreover, formation of the 11-cis isomer is greatly favored for all-trans RPSB when isolated. The very fast photoresponse of visual photoreceptors is thus directly related to intrinsic retinal properties, whereas bacterial rhodopsins tune the excited state potential-energy surface to lower the barrier for particular double-bond isomerization, thus changing both the timescale and specificity of the photoisomerization.
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Project description:Two isoforms of the rat 5alpha-reductase (5alpha-R), the enzyme that converts testosterone into dihydrotestosterone (DHT), and other delta4-3-keto steroids (e.g. progesterone and corticoids) into their 5alpha-reduced metabolites, have been cloned. In this study, a convenient and efficient system was developed to overexpress the two isoenzymes in Saccharomyces cerevisiae by using the ubiquitin-fusion expression system. Two yeast expression vectors have been prepared, YEpR1 and YEpR2, which code for 5alpha-R type 1 and 5alpha-R type 2 respectively; they contain the copper-responsive yeast metallothionein promoter (CUP1) upstream of the ubiquitin coding sequence, and the full-length rat 5alpha-R type 1 or 5alpha-R type 2 cDNAs in frame to the 3' end of the ubiquitin cDNA. The activity of the two isoenzymes produced in yeast was determined in cell lysates at the enzyme pH optima (type 1, pH 7.5; type 2, pH 5.5) and a possible differential intracellular distribution was also evaluated. The kinetic parameters were: type 1, Km 4.6 microM, Vmax.100.6 micrograms/h per mg of protein; type 2, Km 68.6 nM, Vmax. 0.84 micrograms/h per mg of protein. Yeast cell lysates were fractionated by differential centrifugation and the 5alpha-R type 1 activity was maximal in fractions containing nuclei (1000 g and 2500 g), whereas the maximal activity of 5alpha-R type 2 was present in subcellular fractions sedimenting at higher speeds (20000g). The data indicate that yeasts overexpress the two 5alpha-R isoenzymes, maintaining their native biochemical properties, and that the two isoforms are probably differentially localized within the yeast cell.
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Project description:Transcription factors are key regulators in both normal and pathological cell processes. Affecting the activity of these proteins is a promising strategy for understanding gene regulation and developing effective therapeutics. Co(III) Schiff base complexes ([Co(acacen)(L)2](+) where L=labile axial ligands) have been shown to be potent inhibitors of a number of zinc metalloproteins including Cys2His2 zinc finger transcription factors. Inhibition by [Co(acacen)(L)2](+) of the target protein is believed to occur through a dissociative exchange of the labile axial ligands for histidine (His) residues essential for function. Here, we report a series of spectroscopic investigations with model peptides of zinc fingers that elucidate the interaction between [Co(acacen)(L)2](+) complexes and zinc finger transcription factors. Observed changes in NMR chemical shifts and 2D (1)H-(1)H NOESY NMR spectra demonstrate the preference of [Co(acacen)(L)2](+) complexes to coordinate His residues over other amino acids. The conformation of [Co(acacen)(L)2](+) upon His coordination was characterized by (1)H NMR spectroscopy, near-UV CD, and electronic absorption. These studies reveal that the resulting His-coordinated [Co(acacen)(L)2](+) complex possesses an octahedral structure. The effects of [Co(acacen)(L)2](+) complexes on the zinc-finger structure were assessed by the degree of hydrogen bonding (probed by 2D NMR spectroscopy) and secondary-structure profiles measured by far-UV CD. These structural studies demonstrate the ability of [Co(acacen)(L)2](+) complexes to disrupt the ββα structure of zinc fingers, resulting in primarily random-coil conformations. A mechanism is described wherein [Co(acacen)(L)2](+) complexes inhibit zinc finger transcription factor activity through selectively coordinating His residues in the zinc finger by dissociative ligand exchange and disrupting the ββα structural motif required for gene regulation.
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Project description:A series of Schiff bases (3.a-f) bearing benzimidazole moiety was successfully synthesized in ethanol by refluxing Oct-2-ynoic acid (1,3-dihydrobenzimidazole-2-ylidene)amide with substituted amines. Fourier transform infrared (FTIR), ultra violet light (UV-VIS), elemental analysis, proton (1H) and carbon (13C) nuclear magnetic resonance spectroscopy were used to characterize the newly synthesized Schiff bases. Micro dilution method was used to determine the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of the Schiff bases, against 14 human pathogenic bacteria (8 Gram negative and 6 Gram positive) and against 7 fungal strains (5 Aspergillus and 2 Fusarium) representatives. Antimalarial activity against Plasmodium falciparum and antitrypanosomal property against Trypanosoma brucei was studied in vitro at a single dose concentration of the Schiff bases. Cytotoxicity of the Schiff bases was assessed against human cervix adenocarcinoma (HeLa) cells. Results obtained show that the newly synthesized Schiff bases are very potent antimicrobial agents. Gram negative bacteria Klebsiella pneumonia and Escherichia coli were more affected on exposure to Compounds 3.c-f (MIC 7.8 µg/mL) which in turn exhibited more antibacterial potency than nalidixic acid reference drug that displayed MICs between 64 and 512 µg/mL against K. pneumonia and E. coli respectively. The test compounds also demonstrated high cytotoxic effect against Aspergillus flavus and Aspergillus carbonarius as they displayed MFC 7.8 and 15.6 µg/mL. Compound 3.c exhibited the highest fungicidal property from this series with MFC alternating between 7.8 and 15.6 µg/mL against the investigated strains. The malarial activity revealed Compounds 3.c and 3.d as the more potent antiplasmodial compounds in this group exhibiting 95% and 85% growth inhibition respectively. The IC50 of Compounds 3.c and 3.d were determined and found to be IC50 26.96 and 28.31 µg/mL respectively. Compound 3.a was the most cytotoxic agent against HeLa cells in this group with 48% cell growth inhibition. Compounds 3.c, 3.d and 3.f were biocompatible with HeLa cells and displayed low toxicity. With a very low cytotoxic effect against HeLa, compound 3.c stands out to be a very good antiparasitic agent and consideration to further evaluate the candidate drug against others cell lines is necessary.
| S-EPMC6842205 | biostudies-literature
Project description:Biological membranes are complex dynamic systems composed of a great variety of carbohydrates, lipids, and proteins, which together play a pivotal role in the protection of organisms and through which the interchange of different substances is regulated in the cell. Given the complexity of membranes, models mimicking them provide a convenient way to study and better understand their mechanisms of action and their interactions with biologically active compounds. Thus, in the present study, a new Schiff base (Bz-Im) derivative from 2-(m-aminophenyl)benzimidazole and 2,4-dihydroxybenzaldehyde was synthesized and characterized by spectroscopic and spectrometric techniques. Interaction studies of (Bz-Im) with two synthetic membrane models prepared with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and DMPC/1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) 3:1 mixture, imitating eukaryotic and prokaryotic membranes, respectively, were performed by applying differential scanning calorimetry (DSC). Molecular dynamics simulations were also developed to better understand their interactions. In vitro and in silico assays provided approaches to understand the effect of Bz-Im on these lipid systems. The DSC results showed that, at low compound concentrations, the effects were similar in both membrane models. By increasing the concentration of Bz-Im, the DMPC/DMPG membrane exhibited greater fluidity as a result of the interaction with Bz-Im. On the other hand, molecular dynamics studies carried out on the erythrocyte membrane model using the phospholipids POPE (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine), SM (N-(15Z-tetracosenoyl)-sphing-4-enine-1-phosphocholine), and POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) revealed that after 30 ns of interaction, both hydrophobic interactions and hydrogen bonds were responsible for the affinity of Bz-Im for PE and SM. The interactions of the imine with POPG (1-Palmitoyl-2-Oleoyl-sn-Glycero-3-Phosphoglycerol) in the E. coli membrane model were mainly based on hydrophobic interactions.
| S-EPMC8235182 | biostudies-literature