Solvent interactions with the active site of the pig heart cytosolic aspartate aminotransferase.

Aqueous solvent interactions with the chromophoric pyridoxal phosphate prosthetic group of aspartate aminotransferase (EC 2.6.1.1) were analyzed quantitatively with ethylene glycol, glycerol, dimethylsulfoxide (DMSO), sucrose, and xylitol as cosolvents. The smaller cosolvents perturb the visible absorption and visible dichroic spectra of the free enzyme, but this solvent perturbation is not observed with the acidic enzymeglutarate complex. Addition of cosolvents caused an increase in the enzyme's affinity for glutarate. This increase in affinity resulted from an increase in the acidic dissociation constant (pK₂) of the enzyme-glutarate complex. The changes in the acidic dissociation constant of the enzyme-glutarate complex, upon addition of cosolvents, correlate well with the changes observed in the pK_a's of carboxylic acids in comparable solvents. Since these solvents have little effect on the pK_a of the enzyme itself, it is concluded that the increase in affinity is due to a specific solvation effect on a carboxyl group of the enzymebound glutarate, rather than resulting from a conformational change in the protein.     

Effect of methamphetamine on the development of acute morphine tolerance and dependence in mice

The effect of methamphetamine on morphine analgesia (tail-flick assay) was studied in non-tolerant mice and in mice made acutely tolerant to morphine following a single injection of 100 mg/kg morphine. The analgesic potency of morphine was increased in non-tolerant and tolerant mice to the same extent by 3.2 mg/kg methamphetamine (3.3 and 4.4 fold increases, respectively). In contrast, the ED50's for morphine analgesia and naloxone-precipitated jumping in mice pretreated with either 100 mg/kg morphine or both morphine and 3.2 mg/kg methamphetamine were not significantly different, indicating that methamphetamine had no effect on the development of acute morphine tolerance and dependence. Although methamphetamine had no effect on the development of acute tolerance to morphine, 4-day pretreatment with methamphetamine produced cross-tolerance to morphine analgesia. However, cross-tolerance to morphine was not accompanied by enchanced sensitivity to naloxone.     

The explicit analysis of consecutive pseudo-first-order reactions: Application to kinetics of thiolysis of dithiasuccinoyl (Dts) amino acids

An explicit set of general methods for the experimental determination of the rates k₁ and k₂ of consecutive pseudo-first-order reactions is described and discussed. These rely on the direct simultaneous analytical quantitation of the starting material, intermediate, and product of the reaction, and thus differ from present techniques based on measurement of coreactant consumption or coproduct appearance. The quantity $\text{k}{}^{\mathrm{<mtext>env</mtext>}}\text{=}\text{k}{}_1\text{k}{}_2\text{(k}{}_1\text{+ k}{}_2\text{)}$ is shown to define a good “envelope” approximation to product formation according to the simple law 100% [1 ? exp(?k^envt)]. The theory of envelopes is useful for comparing overall rates of reactions with widely differing values of $\text{κ =}\text{k}{}_2\text{k}{}_1$. The kinetic pattern of thiolysis of dithiasuccinoyl amino acids to carbamoyl disulfide intermediates to product free amino acids is analyzed and shown to agree quantitatively with theory.     

Arylhydroxamic acid N,O-acyltransferase. Apparent suicide inactivation by carcinogenic N-arylhydroxamic acids

Carcinogenic arylhydroxamic acids (N-hydroxy-2-acetylamino-fluorene, N-hydroxy-4-acetylaminobiphenyl, and $\text{trans}$-N-hydroxy-4-acetyl-aminostilbene) are irreversible inhibitors of rat and hamster hepatic N,O-acyltransferase. The kinetic characteristics of this inhibition are consistent with suicide inactivation of the enzyme. This finding appears to be the first example of carcinogens serving as suicide substrates for an enzyme system which is responsible for their bioactivation.     

Specific and nonspecific infiltration of sponge matrix allografts by specifically sensitized cytotoxic lymphocytes

Urethane sponges coated with allogeneic or syngeneic cells were implanted subcutaneously into mice and the cytotoxicity of infiltrating host cells was assessed in vitro. First-set allogeneic sponges attracted a population of lymphocytes enriched in cytotoxic T cells directed against the alloantigens in the sponge. If two sponges bearing cells of different H-2 specificity were grafted simultaneously to a single recipient, specifically sensitized cytotoxic cells (SSCL) were found in both sponges directed against both sets of alloantigens, although specific infiltration predominated. If a syngeneic and allogeneic sponge were transplanted, SSCL were found in both the syngeneic sponge and allogeneic sponge. These data are interpreted to suggest that chemotactic substances are elaborated at graft sites which can attract circulating SSCL into sites of inflammation and that those released at the specific site are more attractive for SSCL than are those elaborated at sites of nonspecific rejection or healing. In recipients who had previously been sensitized to alloantigens, second-set grafts were rapidly infiltrated by SSCL directed against the sensitizing antigen. First-set indifferent allografts in sensitized recipients were infiltrated by SSCL directed against the previous alloantigens as well as SSCL directed against its own alloantigens. Syngeneic grafts were not infiltrated by SSCL in presensitized recipients. These data suggest that any alloantigenic stimulus can induce the mobilization from lymphoid depots of preformed SSCL directed against another set of antigens; syngeneic grafts cannot. Once mobilized, however, circulating SSCL can respond to specific and nonspecific chemotactic factors elaborated by either healing or rejecting grafts.     

Neurite extension by peripheral and central nervous system neurons in response to substratum-bound fibronectin and laminin

Small groups of blastoderm cells were transplanted from wild-type donor embryos into genetically marked host embryos of the same age. Donor cells were injected either into an homologous or an ectopic region of the recipient, and both donor and recipient embryos were allowed to develop. Donor flies were examined for defects in external structures. Recipients were scored for patches of donor-type marked tissue derived from the injected cells. After ectopic transfer, the donor cells recovered in chimaeric recipients differentiated structures consistent with the donor site of cell removal. No apparent fate change was observed. In the rare cases when both individuals of a donor/host pair survived, a direct correspondence could be made between the deleted region in the donor and the chimaeric patch in the host. The results show that blastoderm cells are stably determined to within a segment.     

Evidence of possible opiate dependence during the behavioral depressant action of a single dose of morphine

Rats were trained to lever press for food pellets under a 20 response fixed ratio (FR 20) schedule of reinforcement. A single injection of 15 mg morphine SO₄/kg suppressed operant behavior for $\text{1}\text{1}\text{2}\text{–3}\text{1}\text{2}\text{hrs}$, after which time responding resumed at a reduced rate. When 0.25 mg naloxone HCl/kg was given during the recovery phase, the behavioral depressant effect of the narcotic was immediately reversed and operant performance returned to predrug rates. In contrast, when 0.5 mg naloxone/kg was given at this time, operant behavior was abolished for at least 1 hr. Naloxone, at these doses, did not affect responding in drug-naive subjects. These results suggest that a single, relatively low dose of morphine can induce transient dependence which is detectable for several hrs after drug administration, at a time when the acute pharmacological actions of morphine are still apparent.     

Long Noncoding RNAs AC009014.3 and Newly Discovered XPLAID Differentiate Aggressive and Indolent Prostate Cancers

INTRODUCTION: The molecular mechanisms underlying aggressive versus indolent disease are not fully understood. Recent research has implicated a class of molecules known as long noncoding RNAs (lncRNAs) in tumorigenesis and progression of cancer. Our objective was to discover lncRNAs that differentiate aggressive and indolent prostate cancers. METHODS: We analyzed paired tumor and normal tissues from six aggressive Gleason score (GS) 8-10 and six indolent GS 6 prostate cancers. Extracted RNA was split for poly(A)+ and ribosomal RNA depletion library preparations, followed byRNA sequencing (RNA-Seq) using an Illumina HiSeq 2000. We developed an RNA-Seq data analysis pipeline to discover and quantify these molecules. Candidate lncRNAs were validated using RT-qPCR on 87 tumor tissue samples: 28 (GS 6), 28 (GS 3+4), 6 (GS 4+3), and 25 (GS 8-10). Statistical correlations between lncRNAs and clinicopathologic variables were tested using ANOVA. RESULTS: The 43 differentially expressed (DE) lncRNAs between aggressive and indolent prostate cancers included 12 annotated and 31 novel lncRNAs. The top six DE lncRNAs were selected based on large, consistent fold-changes in the RNA-Seq results. Three of these candidates passed RT-qPCR validation, including AC009014.3 (P < .001 in tumor tissue) and a newly discovered X-linked lncRNA named XPLAID (P = .049 in tumor tissue and P = .048 in normal tissue). XPLAID and AC009014.3 show promise as prognostic biomarkers. CONCLUSIONS: We discovered several dozen lncRNAs that distinguish aggressive and indolent prostate cancers, of which four were validated using RT-qPCR. The investigation into their biology is ongoing.     

Cholinesterase enzymes in the blood of patients with Alzheimer's disease

Plasma pseudocholinesterase activity was about 100% higher in patients with Alzheimer's-type dementia than in similar age controls. Red cell acetylcholinesterase activity tended to be lower in patients than controls. Administration of lecithin substantially increased plasma choline levels but did not alter activity of either of the cholinesterase enzymes.     

Selenium detoxification of heavy metals: a possible mechanism for the blood plasma

Among the activities of the essential trace element selenium is the ability to reduce the toxicity of heavy metal ions like cadmium(II) and mercury(II). Detoxification often depends on the metabolic reduction of selenium to hydrogen selenide; the mechanism generally advanced to explain such selenium/metal interactions is that selenide combines with heavy metal ions to give a metal selenide which is metabolically inert. However, this hypothesis does not consider circumstances where selenide is quickly removed by other reactions. Given the ease with which selenide is oxidized, such conditions are likely to occur in the blood plasma, an environmental rich in oxidizing agents and a site for many selenium/metal interactions. Using polarography to monitor both selenide and cadmium, we have found that selenide reacts rapidly in vitro with the disulfide bonds present in bovine serum albumin in preference to forming cadmium selenide. We hypothesize that a similar reaction occurs in the blood plasma with the disulfide bonds of plasma proteins to generate thiol groups on the protein involved, and that these newly formed thiols are responsible for the observed reduction of metal toxicity through the ability to chelate heavy metal ions.     

The interaction of methylcobalamin with tetracyanoplatinate(II), tetrathiocyanoplatinate(II) and tetrachloroplatinate(II)

The interactions of methylcobalamin (CH₃-B₁₂) with Pt(CN)₄^2?, PtCl₄^2?, and Pt(SCN)₄^2? in aqueous solution were studied by UV-visible and ¹H NMR spectroscopy. Together with earlier results on the mechanism of the Pt(IV)-dependent methyl-transfer reaction from CH₃-B₁₂ to Pt(II), these studies suggest at least three Pt binding sites on CH₃-B₁₂. One site, which is occupied by all three complexes (K₁ = 4 X 10³ M^?1 for Pt(CN)₄^2? and 3 X 10³ M^?1 for PtCl₄^2?), is located on the CoCH₃ side of the corrin macrocycle, and is involved in the methyl-transfer process in the presence of a Pt(IV) complex. An additional site for Pt(SCN)₄^2? is the N-3 of the benzimidazole group, resulting in dissociation of this group from the cobalt. An additional site for Pt(CN)₄^2? has a binding constant of 16 M^1? and ¹H NMR changes indicate perturbation but not dissociation of the benzimidazole group. Only the first interaction is discerned for PtCl₄^2?.     

Ascorbic acid modulation of splenic cell cyclic GMP metabolism.

Chronic ascorbate deprivation of guinea pigs decreased splenic cell cyclic GMP levels (80%); ascorbate (1 mM) addition to these cells $\text{in vitro}$ restored the cellular concentration to control levels. Splenic cells from non-scorbutic animals also exhibited increases in cyclic GMP levels in response to exogenous ascorbate whereas thiol reducing agents diminished cellular cyclic GMP concentration. Agents that inhibit the propagation of free radicals prevented this cellular effect of ascorbate while agents known to interfere with or promote H₂O₂ production had no effect. Guanylate cyclase activity in cell lysates increased after treatment of intact cells with ascorbate; dithiothreitol reversed this effect. Ascorbate also enhanced guanylate cyclase activity in cell lysates. The results suggest that oxidizing equivalents in the form of the monoanionic free radical of ascorbate alter cyclic GMP metabolism in these cells by activating guanylate cyclase via a mechanism involving oxidation of a cyclase-related component.     

The cellular basis of adjuvant arthritis: II. Characterization of the cells mediating passive transfer

It has previously been reported that lymph node or spleen cells from rats with adjuvantinduced arthritis can transfer the disease to normal recipients after being cultured with concanavalin A (Con A). In this report, it is shown that a subpopulation of cells that (1) lack surface Ig and the antigen reactive with the monoclonal antibody OX8, (2) are largely nonadherent and esterase negative, and (3) are predominantly marked by the monoclonal antibody W3/25 can transfer arthritis after stimulation with Con A. Adjuvant-sensitized lymph node or spleen cells stimulated with Con A but not PHA transfer arthritis, and this difference correlates with relatively higher levels of interleukin 2 secretion by Con A-stimulated cells. A synthetic adjuvant, CP-20961, a substituted propanediamine, induces arthritis that is passively transferable under the same conditions as arthritis induced by classical mycobacterium-containing adjuvant. The data support the hypothesis that adjuvant inoculation in the rat results in the induction of a unique subpopulation of T cells that initiate the inflammatory joint disease.     

Amino acid sequencing by gas chromatography-mass spectrometry using trifluoro-dideuteroalkylated peptide derivatives: C. The primary structure of the carboxypeptidase inhibitor from potatoes

The carboxypeptidase inhibitor from potatoes has been used to demonstrate the utility of gas chromatography-mass spectrometry for the determination of the primary structure of such large polypeptides. Two mixtures of oligopeptide fragments, obtained by limited acid hydrolysis and enzymatic digestion of this polypeptide, were transformed into the corresponding mixtures of O-trimethyl-silylated trifluoro-dideuteroethyl polyamino alcohols which were then analyzed by gas chromatography-mass spectrometry. The resulting mass spectral and retention index data allowed the identification of 61 oligopeptide fragments which were assembled by the computer by positioning all 39 amino acid residues in a unique sequence (with the exception of the assignment of the primary amide groups of Asn and Gln).     

Teratoma cybrids: An analysis of the post-fusion effects of myoblast cytoplasms on embryonal carcinoma cells

The influence of rat myoblast cytoplasms in cybrids derived from fusions with mouse embryonal carcinoma cells (EC cells) has been considered. Cytoplasmic hybrids (cybrids) were identified by the use of nuclear and cytoplasmic markers. The presence of chromocenters was used as a marker for EC-cell nuclei. Phagocytosed polystyrene beads served as cytoplasmic markers. Shortly after fusion the cybrids had a drastically altered morphology. They lacked the cytoplasmic lipid granulum characteristic of EC cells and had gained demonstrable fibronectin deposits. These phenotypic changes disappeared during a 3-day period after fusion as the cybrids gradually regained normal EC-cell properties. It was considered that the lack of more stable phenotypic modifications in the cybrids was related to major abnormalities in the cytoplasm preparations. However, cytoplasms were found to be viable for up to 65 h post-enucleation and, as analysed by 2-D gel electrophoresis, continued to synthesize the same major polypeptides as did intact cells, for at least 10 h. Thus, the addition of a myoblast cytoplasm to an EC cell has significant short-term effects but has no detectable permanent or heritable effect on the EC phenotype.     

Some indications for inverse DNA duplication

The Continuum Model postulates that preparations for the initiation of DNA synthesis takes place continuously, and in all phases of the cell cycle. There are no G1-specific events involved in the initiation of DNA synthesis. The statistical predictions of the Continuum Model are now presented with four basic variables: (1) the rate of initiator synthesis, (2) the time for passage through the replication-segregation sequence, (3) the amount of initiator required for initiation of DNA synthesis in a particular cell, and (4) the variation in equipartition of cells at division. Computer simulations reveal that the Continuum Model is consistent with both α-and β-curves, as well as the quartile test for β-curves. It also explains sister-sister correlations, and the correlations between cell mass at various times in the division cycle and cell interdivision times. With one additional parameter, the Continuum Model can also explain mother-daughter correlation. The Continuum Model accounts for the statistical data which has previously been used to support the Transition-Probability Model. It has a simple biochemical basis, and can explain the observed biochemical and biological observations of cell growth and division.     

Fusion of neurohypophyseal membranes in vitro

Freeze cleaving electron microscopy has shown that fusion of isolated secretory vesicles from bovine neurohypophyses was induced by Ca²⁺ in micromolar concentrations. Mg²⁺ and Sr²⁺ were ineffective. Mg²⁺ inhibited Ca²⁺-induced fusion.In suspensions containing secretory vesicles as well as sheets of cell membrane, release of vasopressin parallel to intervesicular fusion of secretory vesicles with sheets of cell membrane was observed after exposure to Ca²⁺. Mg²⁺ and Sr²⁺ were ineffective in replacing Ca²⁺ as trigger for fusion or vasopressin release.Intervesicular fusion and exocytotic profiles were observed when isolated neurohypophyses or neurosecretosome were exposed to cold.