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PubMed1975

Gas-liquid chromatographic studies of reactions and structural relationships of steroids. Part III. 11alpha-hydroxysteroids of the androstane and pregnane series.

Qualitative and quantitative effects of classical reactions on steroids observed by gas-liquid chromatography (GLC) under standardized conditions, including the double internal-standard technique, are reported. Simple procedures applicable to nanogram amounts of reactants which afford excellent yields of the major products are described. Reactions studied include the Wolff-Kishner removal of keto groups, their conversion into hydroxyl groups with sodium-ethanol or sodium borohydride and into dioxolone derivatives with ethylene glycol; the conversion of hydroxyl into keto groups with chromium trioxide and to trimethylsilyl (TMS) ethers by hexamethyldisilazane; the hydrolysis of dioxolone and TMS derivatives by H+. Gas-liquid chromatograms of reaction mixtures of single- and multistep reactions readily provide information on the effects on the 11alpha-hydroxy and other functional groups at positions 3 and 17 (androstane series) and positions 3 and 20 (pregnane series), and the retention times of many steroids unavailable from commercial or other sources. GLC data analysis provides relationships between steroid structure and retention time from which methods for the computation of retention times and for steroid identification are designed. The accuracy of the calculation methods is demonstrated.

11-Hydroxycorticosteroids↗
PubMed1976

Isolation of brain endopeptidases: influence of size and sequence of substrates structurally related to bradykinin.

Two thiol-activated endopeptidases with pH optima near pH 7.5 were isolated from the supernatant fraction of rabbit brain homogenates by DEAE-cellulose chromatography, gel filtration and isoelectrofocusing. Peptide bond hydrolysis was measured quantitatively by ion-exchange chromatography with an amino acid analyzer. Brain kininase A hydrolyzes the Phe5-Ser6 peptide bond in bradykinin (Bk), Arg1-Pro2-Pro3-Gly4-Phe5-Ser6-Pro7-Phe8-Arg9. It is isoelectric near pH 5.2 and has a molecular weight of approximately 71 000. The enzyme also hydrolyzes the Phe-Ser peptide bond in Lys-Bk, Met-Lys-Bk, des-Arg1-Bk, Lys9-Bk, Pro-Gly-Phe-Ser-Pro-Phe-Arg, and Gly-Pro-Phe-Ser-Pro-Phe-Arg, but does not hydrolyze (0.1%) this bond in des-Phe8-Arg9-Bk. Brain kininase B hydrolyzes the Pro7-Phe8 peptide bond in Bk. It is isoelectric at pH 4.9 and has a molecular weight of approximately 68 000. Brain kininase B also hydrolyzes the Pro-Phe bond in Lys-Bk, Met-Lys-Bk, Lys9-Bk, Ser-Pro-Phe-Arg, and Phe-Ser-Pro-Arg. Pretreatment of denatured kininogen with brain kininase A or B did not reduce the amount of trypsin-releasable Bk from this precursor protein, indicating that the Bk sequence, when part of a large protein, is not a substrate for either enzyme. However, kininase A and B hydrolyze the octadecapeptide Gly-Leu-Met-Lys-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg-Ser-Val-Gin-Val. The data show that a large part of the C-terminal portion of bradykinin is important for the brain kininase A activity and, for both enzymes, the size of the peptide and presumably the residues adjacent to the scissle bond are important in determining the rate of peptide bond hydrolysis by these endopeptidases.

Amino Acid Sequence↗
PubMed1975

The antibody-enzyme analogy. Characterization of antibodies to phosphopyridoxyltyrosine derivatives.

Stable analogs of the crucial Schiff base intermediate of enzymatic and nonenzymatic pyridoxal phosphate catalysis have been used as haptens for induction of specific antibodies. N-(5-phosphopyridoxyl)-3'-amino-L-tyrosine and its conformationally distinct cyclized derivative resemble the Schiff base formed upon mixing tyrosine with pyridoxal phosphate. These compounds were covalently coupled to a protein carrier via the 3'-amino group so as to confer a prescribed orientation, with the coenzyme region farthest removed from the carrier. A third antigen, with the phosphopyridoxyl group alone as the hapten, was prepared by linkage of pyridoxal phosphate directly to free amino groups on the carrier protein. Antibodies elicited for each determinant were purified by means of appropriate affinity columns. Antibody heterogeneity was observed in that different species could be separated from a given serum by sequential elution from the affinity columns with 1 M sodium phosphate buffers of pH 7.6, 5.2, 2.6 and 1.5. In assays of quantitative precipitation, inhibition of precipitation, equilibrium dialysis, and fluorescence quenching, antibodies to the phosphopyridoxyltyrosine haptens showed specificity for the phosphorylated form of the coenzyme and binding activity for both the coenzyme and tyrosine portions of the hapten. Antibodies to the phosphopyridoxyl groups alone did not display a similar reactivity toward the tyrosine portion of the complex haptens. The cyclic and noncyclic conformations of the hapten were serologically distinct, as antibody to each reacted preferentially with the homologous form.

Animals↗
PubMed1976

Clonidine and related analogues. Quantitative correlations.

Twenty-two structural derivatives of clonidine [2-(2,6-dichlorophenylimino)imidazolidine] have been synthesized and their main physicochemical parameters (log P, deltaRM, pKa) determined. Quantitative correlations between the peripheral alpha-mimetic action (pithed rats) and physicochemical parameters pointed out the critical role of the steric effect in the ortho positions. On the other hand, attempted quantitative correlations between physicochemical parameters and central hypotensive activity were unsuccessful. These results are discussed in the light of the postulated mechanism of action of clonidine.

Adrenergic alpha-Agonists↗
PubMed1975

Structural features of double-stranded polyribonucleotides required for immunological specificity and interferon induction.

Purified antibody to poly(adenylic acid)-poly(uridylic acid) was used in quantitative microcomplement fixation assays to detect conformational variations among several double-helical polyribonucleotide analogs of poly(adenylic acid)-poly(uridylic acid) or poly(inosinic acid)-poly(cytidylic acid) that had been previously evaluated for their ability to induce interferon. Modification at the furanose 2'-position of one or both strands resulted in a dramatic decrease in serological reactivity. Most modifications of the bases caused smaller serological changes, and no base modification caused complete loss of reactivity. The reaction patterns support the conclusion that the structure of the furanose and the overall conformation of the helix are critical in the formation of antigenic determinants. The backbones of both strands appear to be involved in forming a single antigenic site, and base modifications may alter the steric relationship between the backbones. In addition, the same structural changes that substantially alter recognition by antibody also lead to large changes in the interferon-inducing ability of the nucleic acid.

Antigen-Antibody Reactions↗
PubMed1976

Human alpha-fetoprotein as a modulator of human lymphocyte transformation: correlation of biological potency with electrophoretic variants.

Human alpha-fetoprotein (HAFP) isolated by immunoadsorbent column was shown to suppress the mitogenic response of human lymphocytes to phytomitogens, antihuman thymocyte antiserum, and the mixed lymphocyte culture. HAFP isolated from the sera and ascitic fluid of five hepatoma patients, and from fetal liver, varied in biological potency over three orders of magnitude. Extended agarose gel electrophoresis and crossed immunoelectrophoresis demonstrated three molecular species of HAFP. Quantitation of the three species revealed a correlation between the relative amount of the most negatively charged species and biological potency. Treatment of HAFP with neuraminidase to remove completely sialic acid residues did not alter the biological potency, but converted the three species to two species having slower electrophoretic mobilities. We conclude that differences in sialic acid content are only partly responsible for the microheterogeneity demonstrated by HAFP, and that variability in another charged moiety is also present. Variation in the relative proportions of the different molecular species of HAFP may be important in the regulation of its immunosuppressive properties.

Carcinoma, Hepatocellular↗
PubMed1978

New observations concerning the chloroacetaldehyde reaction with some tRNA constituents. Stable intermediates, kinetics and selectivity of the reaction.

The stable intermediates formed in the reaction of cytosine, cytidine and adenosine with chloracetaldehyde were isolated. The -CH2CH/OH/- bridge between the exo and endo nitrogen atoms of the parent base was found in these compounds by means of PMR spectroscopy. Their acid-induced dehydration resulted in formation of appropriate ethenoderivatives. The rate constants of the intermediate formation and its dehydration were found to be 38x10(-4) and 47x10(-4) /min-1/ for adenosine, and 33x10(-4) and 10x10(-4) /min-1/ for cytidine. The PH range of 4.5--5.0 was found to be optimum for both adenosine and cytidine reactions. The quantitative modification of these two nucleosides in the presence of guanosine may be achieved with high selectivity only at a low pH of 3.0--4.0 N6-methyladenosine and N4-methylcytidine react quantitatively with chloroacetaldehyde and the reaction rate is higher than in the case of the parent nucleosides. The structure of the reaction products was assigned on the basis of PMR spectroscopy.

Acetaldehyde↗
PubMed1978

Recognition of individual procaryotic and eucaryotic transfer-ribonucleic acids by B subtilis adenine-1-methyltransferase specific for the dihydrouridine loop.

Bulk tRNA from yeast and Rat liver can be methylated in vitro with -adenosylmethionine and B, subtilis extracts. The sole product formed is 1-methyladenosine (m1A). This tRNA (adenine-1) methyltransferase converts quantitatively the 3'-terminal adenosine-residue in the dihydrouridine-loop of tRNAThr and tRNATyr from yeast into m1A. Out of 16 eucaryotic tRNAs with known sequences 6 accepted methyl groups, all at a molar ratio of 1. These tRNAs have in common an unpaired adenosine-residue at the specific site in the sequence Py-A-A+-G-G-C-m2G. Out of 12 tRNAs from E. coli 6 served as specific substrates. These E. coli tRNAs also have an unpaired adenosine-residue at the 3'-end of the D-loop. Besides restrictions in primary structure intact secondary and tertiary structure is important for recognition of the specific tRNAs by the enzyme.

Bacillus subtilis↗
PubMed1977

Spontaneous deamidation of a protein antibiotic, neocarzinostatin, at weakly acidic pH. Conversion to a homologous inactive preneocarzinostatin due to change of asparagine 83 to aspartic acid 83 accompanied by conformational and biological alterations.

The amide content of neocarzinostatin (NCS), an antitumor protein, has been determined by analysing asparagine and glutamine in the Pronase-aminopeptidase M digests of tetra-S-carboxymethyl-NCS and carboxyl-modified NCS (modified with a water-soluble carbodiimide and [14C]glycine methyl ester). Preneocarzinostatin (PRE) was separated and purified from a crude NCS preparation by CM-cellulose column chromatography. PRE was found to contain one mole less asparagine than NCS, and asparagine was deamidated to aspartic acid in PRE. A time-dependent conversion of NCS to PRE at pH 3.2 at 4 degrees or in 0.1 M acetic acid at 26 degrees was studied in two ways; first, by quantitative determination of NCS and PRE by CM-cellulose column chromatography and second, by following the release of free NH3 during dialysis in an air-tight container. Within experimental error, PRE was indistinguishable from NCS in amino acid content after acid hydrolysis, as well as in apparent molecular weight as determined by SDS-disc gel electrophoresis (10% acrylamide), and N- and C-terminal amino acid residues. Both NCS and PRE shared a common antigenicity as determined by Ouchterlony's agar diffusion method. Only a slight difference between the two in electrophoresis on a cellulose acetate membrane and on a peptide map of the tryptic digest was demonstrated. PRE, however, was completely devoid of biological activity. In addition to the chromatographic difference, a conformational difference was observed by CD spectroscopy, namely, an apparently looser structure of PRE was indicated by the shallowness of the trough in the 240-265 nm region. This interpretation was supported by the finding that digestions by Pronase were more extensive with PRE than with NCS. These results indicate an important role of the single asparagine residue (Asn 83) of NCS in the biological activity, which is evidently governed by the conformation.

Amino Acids↗
PubMed1977

Intramolecularly-quenched fluorescent peptides as fluorogenic substrates ofleucine aminopeptidase and inhibitors of clostridial aminopeptidase.

Fluorogenic oligopeptide derivatives of the type Lys(ABz)-ONBzl, where ABz iso-aminobenzoyl (anthraniloyl), X stands for Ala Phe, or Ala-Ala, and ONBzlis p-nitrobenzyloxy, were synthesized and shown to be hydrolyzed by leucine aminopeptidase. The hydrolysis is accompanied by an increase in fluorescence due to disruptionof the intramolecular quenching of the fluorescent anthraniloyl moiety by the nitrobenzyester group. The spectral characteristics of the compounds are not consistent withan energy transfer mechanism according to Förster, therefore the quenching isassumed to be caused by a direct encouter between the quenching and the fluorecentgroups. The change in fluorescence that accompanies the enzymic hydrolysis ofthe first peptide bound was used for quantitative measurement of the activity ofthe activity of leucine aminopeptidase and for the determination of some of itskinetic parameters. A bacterial aminopeptidase from Clostrdium histolyticumthat is very similar to leucine aminopeptidase in its substrate specificity inits substrate specificity did not hydrolyze the above peptidederivatives. Thehydrolysis of leucine p-nitroanilide by this enzyme was found to be inhibitedby the three peptides and the corresponding inhibition constants were determined.

Aminopeptidases↗
PubMed1975

Characterization of bleomycin action on DNA.

Cleavage of SV40 DNA by bleomycin was assayed quantitatively in vitro in the presence of various ppolynucleotides. SV40 DNA was protected from bleomycin- duced cleavage by native or denatured DNA of other origins, oly dG-C.poly dG-C, poly dA-T.poly dA-T and poly dA-T (denatured) but not by tRNA of E. coli, apurinic acid, poly dA, poly dT and various deoxyribooligonucleotides. Various bleomycins and their derivatives and various fragments of bleomycin were tested for possible activity in cleaving SV40 DNA and from the results some structure-activity relationships for the action of bleomycin to act on DNA were outlined. Actinomycin D stimulated bleomycin action while ethidium bromide inhibited it.

Animals↗
PubMed1975

Use of 5-deazaFAD to study hydrogen transfer in the D-amino acid oxidase reaction.

The apoprotein of hog kidney D-amino acid oxidase was reconstituted with 5-deazaflavin adenine dinucleotide (5-deazaFAD) to yield a protein which contains 1.5 mol of 5-deazaFAD/mol of enzyme. The deazaFAD-containing enzyme forms complexes with benzoate, 2-amino benzoate, and 4-aminobenzoate which are both qualitatively and quantitatively similar to those observed with native enzyme. The complex with 2-aminobenzoate exhibits a new long wavelength absorption band characteristic of a flavin charge-transfer complex. The reconstituted enzyme exhibits no activity when assayed by D-alanine oxidation. However, the bound chromophore can be reduced by alanine, phenylalanine, proline, methionine, and valine, but not by glutamate or aspartate, indicating the deazaFAD enzyme retains the substrate specificity of the native enzyme. Reduction of the enzyme by D-alanine exhibits a 1.6-fold deuterium isotope effect. Reoxidation of the reduced enzyme occurred in the presence of pyruvate plus ammonia, but not with pyruvate alone or ammonia alone. beta-Phenylpyruvate and alpha-ketobutyrate, but not alpha-ketoglutarate could replace pyruvate. Reduced enzyme isolated following reaction with [alpha-3H]alanine was found to contain 0.5 mol of tritium/mol of deazaFADH2. After denaturation of the tritium-labeled enzyme, the radioactivity was identified as deazaFADH2. Reaction of the reduced tritium-labeled enzyme with pyruvate plus ammonia prior to denaturation yields [alpha-3H]alanine and unlabeled deazaFAD. These results suggest that reduction and reoxidation of enzyme-bound deazaFAD involves the stereo-specific transfer of alpha-hydrogen from substrate to deazaFAD.

Aminobenzoates↗
PubMed1979

Nonlinear dependence of biological activity on hydrophobic character: the bilinear model.

In homologous series of compounds biological activity is linearly dependent on hydrophobic character until a cut-off point is reached where this linear relationship changes to a nonlinear relationship: biological activity increases with increase of hydrophobic character, reaches a maximum and then decreases with further increase of hydrophobic character. Drug transport in biological systems is determined by the rate constants of transfer of the drug through aqueous and organic compartments. In simple in vitro systems the rate constant k1 of transport of a drug from an aqueous phase into an organic phase and the rate constant k2 of the reverse process can be described as functions of the partition coefficient P: log k1 = log P - log (beta P + 1) + c and log k2 = - log (beta P + 1) + c. Observed and calculated k1 and k2 values are used to simulate drug transport in different multicompartment systems. Based on the McFarland probability model a new model for the quantitative description of the dependence of biological activity on hydrophobic character, called bilinear model, log 1/C = a log P - b log (beta P + 1) + C, has been derived recently: unsymmetrical curves with linear ascending and descending sides and a parabolic part within the range of optimal lipophilicity result from this model. The bilinear model is applied to experimental data of drug absorption, drug distribution and drug activity in biological systems. A comparison of the parabolic model and the bilinear model shows that in nearly all cases a better fit of the data results from the bilinear model.

Acids↗
PubMed1976

Evidence from 13C NMR for protonation of carbamyl-P and N-(phosphonacetyl)-L-aspartate in the active site of aspartate transcarbamylase.

Nuclear magnetic resonance has been used to study the binding of [13C]carbamyl-P (90% enriched) to the catalytic subunit of Escherichia coli aspartate transcarbamylase. Upon forming a binary complex, there is a small change in the chemical shift of the carbonyl carbon resonance, 2 Hz upfield at pH 7.0, indicating that the environments of the carbonyl group in the active site and in water are similar. When succinate, an analog of L-aspartate, is added to form a ternary complex, there is a large downfield change in the chemical shift for carbamyl-P, consistent with interaction between the carbonyl group and a proton donor of the enzyme. The change might also be caused by a ring current froma nearby aromatic amino acid residue. From the pH dependence of this downfield change and from the effects of L-aspartate analogs other than succinate, the form of the enzyme involved is proposed to be an isomerized ternary complex, previously observed in temperature jump and proton NMR studies. The downfield change to chemical shift for carbamyl-P bound to the isomerized complex is 17.7 +/- 1.0 Hz. Using this value, the relative ability of other four-carbon dicarboxylic acids to form isomerized ternary complexes with the enzyme and carbamyl-P has been evaluated quantitatively. The 13C peak for the transition state analog N-(phosphonacetyl)-L-aspartate (PALA), 90% enriched specifically at the amide carbonyl group, is shifted 20 Hz downfield of the peak for free PALA upon binding to the catalytic subunit at pH 7.0. In contrast, the peak for [1-13C] phosphonaceatmide shifts upfield by about 6 Hz upon binding. Since PALA induces isomerization of the enzyme and phosphonacetamide does not, these data provide further evidence consistent with protonation of the carbonyl group only upon isomerization. The degrees of protonation is strong acids of the carbonyl groups of PALA, phosphonacetamide and urethan (a model for the labile carbamyl-P) have been determined, as have the chemical shifts for these compounds upon full protonation. From these data it is calculated that the amide carbonyl groups of carbamyl-P and PALA might be protonated to a maximum of about 20% in the isomerized complexes at pH 7.0. The change in conformation of the enzyme-carbamyl-P complex upon binding L-aspartate, previously proposed to aid catalysis by compressing the two substrates together in the active site, may be accompanied by polarization of the C=O bond, making this ordinarily unreactive group a much better electrophile. A keto analog of PALA, 4,5-dicarboxy-2-ketopentyl phosphonate, also binds tightly to the catalytic subunit and induces a very similar conformational change, whereas an alcohol analog, 4,5-dicarboxy-2-hydroxypentyl phosphonate, does not bind tightly, indicating the critical importance of an unhindered carbonyl group with trigonal geometry.

Aspartic Acid↗