Histochemical analysis of alcohol-lability and effects of inorganic ions on the metachromasia of galactogen

Summary Galactogen localised in the albumen gland of a land snail exhibited an intense and selective metachromatic reaction with azure A at pH 3.5 to 5.5. The metachromasia was labile towards alcoholic treatment. Methanol, ethanol, n-propanol and n-butanol in this order abolished the metachromasia with increasing efficiency. An interesting relationship between the capacity to abolish the galactogen metachromasia and the dielectric constants of these alcoholic solvents was also observed. The higher the dielectric constant of an alcohol the lower was its capacity to suppress the metachromasia of galactogen. Inorganic ions also suppressed the metachromasia of galactogen. Their capacity to suppress the metachromasia was a linear function of the charge carried by them. The pH dependence, effects of alcohol treatment and inorganic ions on the metachromasia of galactogen are considered in comparison with that of sulfomucins, sialomucins and hyaluronic acid. The importance of metachromasia techniques in the histochemical detection of galactogen is described.     

Effects of Ethanol on the Metachromatic Reaction of Toluidine Blue O

Ethanol abolishes the metachromatic reaction of toluidine blue O with un-combined chromotropes but not when they are in association with protein. The green colour obtained in metachromatic regions is established as not due to any green impurity of the dye by chromatographic analysis but due to the fluid dehydrants combining with the dye as dye-organic solvent mixture showed green. The loss of metachromasia is not due to a dehydration effect of ethanol alone for the following reasons: (i) Stained samples of chromotropes dried in vacuuo continued to retain the metachromatic colour, (ii) Although other dehydrating agents likewise abolished the metachromasia, alcohols which have very slight affinity to water also abolished it, (iii) Ethanol does not abolish metachromasia produced in an acid mucopolysaccharide-protein complex. This has been suggested as due to the inability of ethanol to separate the dye from such compounds and to bring about a shift to green.     

Microbial formation of esters

Small aliphatic esters are important natural flavor and fragrance compounds and have numerous uses as solvents and as chemical intermediates. Besides the chemical or lipase-catalyzed formation of esters from alcohols and organic acids, small volatile esters are made by several biochemical routes in microbes. This short review will cover the biosynthesis of esters from acyl-CoA and alcohol condensation, from oxidation of hemiacetals formed from aldehydes and alcohols, and from the insertion of oxygen adjacent to the carbonyl group in a straight chain or cyclic ketone by Baeyer–Villiger monooxygenases. The physiological role of the ester-forming reactions can allow degradation of ketones for use as a carbon source and may play a role in detoxification of aldehydes or recycling cofactors. The enzymes catalyzing each of these processes have been isolated and characterized, and a number of genes encoding the proteins from various microbes have been cloned and functionally expressed. The use of these ester-forming organisms or recombinant organisms expressing the appropriate genes as biocatalysts in biotechnology to make specific esters and chiral lactones has been studied in recent years.     

Secondary solvent effects on the circular dichroism spectra of polypeptides in non-aqueous environments: influence of polarisation effects on the far ultraviolet spectra of alamethicin

Secondary solvent effects on the far ultraviolet circular dichroism spectra of the polypeptide alamethicin have been studied systematically in a series of alcohols. The magnitudes of the shifts have been correlated with the physical properties of the solvents in an attempt to discover the underlying physical principles responsible for these shifts. The solvent effect in non-aqueous solvents generally produces spectral transitions with peaks found at longer wavelengths than those in aqueous solution, and is correlated with increasing refractive indices and with decreasing dielectric constants of the solvents. It appears that polarisation effects are the major contributors to the interactions between the chromophore and solvent molecules, and hence give rise to the red shift. It is clear that this secondary solvent effect is an important factor which should be considered in the examination and estimation of polypeptide secondary structures in non-aqueous solvents and membranes.     

Studies on immobilized trypsin in high concentrations of organic solvents.

Trypsin was covalently immobilized on porous glass in the presence and absence of a specific substrate and reacted in various organic solvents of different dielectric constants. Optimum solvent concentration, pH profile, Km(app), Vmax(app), productivity versus temperature, activity, and reaction rates were determined. Reaction rates of six lysyl dipeptides were compared. Crystalline trypsin was dansylated for studies by nanosecond fluorescence techniques to determine the effects of introducing high concentrations of organic solvents on the molecule. The results indicated that greater reaction rates were observed with dipeptides having more acidic carboxyl terminal groups. The data also indicated that greater reaction rates were observed in higher concentrations of solvents of lower dielectric constants. Nanosecond fluorescence spectroscopy of trypsin in high concentrations of a low dielectric constant solvent indicated major dehydration even though maximal enzyme activity was achieved under these conditions.     

Solvent effects on biocatalysis in organic systems: equilibrium position and rates of lipase catalyzed esterification

Porcine pancreatic lipase immobilized on celite particles has been employed as a catalyst for the esterification of dodecanol and decanoic acid in a predominantly organic system. Solvent influence on the equilibrium position and on the catalyst activity has been studied using 20 solvents, including aliphatic and aromatic hydrocarbons, ethers, ketones, nitro- and halogenated hydrocarbons, and esters. The equilibrium constant for esterification correlates well with the solubility of water in the organic solvent, which in turn shows a good relationship with a function of Guttman's donor number and the electron pair acceptance index number of the solvent. This may be rationalized in terms of the requirements for solvation of water and of the reactants. The catalyst activity, measured as the initial rate of the esterification reaction, is best correlated as a function of both n-octanol-water partition coefficient (log P) and either the electron pair acceptance index or the polarizability.     

Transprotection of silyl ethers of nucleosides in FeCl3 based ionic liquids

Ionic liquid mediated deprotection of tert-butyldimethyl silyl (TBDMS) ethers derived from various primary and secondary alcohols have been studied and the reaction conditions optimized. Deprotection of the silyl ethers in FeCl3 based ionic liquids in presence of acetic anhydride yielded the acetate esters of the corresponding alcohols in good yields. The transprotection methodology was extended to the silyl ethers of nucleosides to yield the corresponding acetylated products.     

Probing the interactions of alcohols with biological membranes with the fluorescent probe Prodan.

Prodan [6-propionyl-2-(dimethylamine)naphthalene] is a hydrophobic fluorescent probe which is extremely sensitive to both the polarity and the hydrogen-bond donating capacity of the solvent. In binary mixtures of solvents, the hydrogen-bond donating effect on Prodan fluorescence saturates at relatively low concentrations of protic solvent while the polarity effect is proportional to the mixture's dielectric constant. The fluorescence emission maximum is approximately a linear function of the dielectric constant in both protic and aprotic solvents, and this allows estimation of the dielectric constant in both environments. In phospholipid bilayers and biological membranes, Prodan exhibits two distinct emission peaks: blue (430-445 nm) and green (470-505 nm). Temperature determines the relative intensity of the two peaks, but their wavelengths depend on the type of membrane and appear to reflect a specific membrane environment. In phospholipid vesicles, alcohols reduce the fluorescence intensity of the blue peak and produce a red-shift in the emission maximum of the green peak. Taking the partition coefficients of the alcohols into account, short-chain alcohols are much more effective than longer-chain alcohols in red-shifting the emission maximum of the green peak. Alcohols have similar effects on Prodan fluorescence in liver microsomal and mitochondrial membranes, synaptosomal membranes, and red blood cell plasma membranes. However, in liver organelle membranes the red-shift of the green peak is the dominant effect while in plasma membranes the quenching of the fluorescence of the blue peak is dominant. These effects are observed at low (pharmacological) ethanol concentrations and provide a unique tool for probing the interactions of ethanol with biological membranes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of metabolic cooperation in Chinese hamster V79 cells by various organic solvents and simple compounds

Gap-junctional intercellular communication is a biological process implicated in the regulation of cell proliferation and differentiation. Metabolic cooperation between 6-thioguanine-sensitive and resistant Chinese hamster cells, in vitro, has been used as a means to detect chemicals which can inhibit this form of intercellular communication. To further characterize this in vitro system as a potential screening assay for potential teratogens, tumor promoters and reproductive toxicants, a series of common solvents as well as other chemicals representing eight different functional groups, i.e., alcohols with straight or side chains, glycols, ketones, esters, ethers, phenols, aldehydes, amines and amino compounds and oxygen-heterocyclic compounds, were tested for their ability to inhibit colony-formation and to inhibit metabolic cooperation. A wide range of effects were observed which suggested a structure/activity relationship between a chemical's ability to inhibit gap junction-mediated intercellular communication and the cytotoxicity of a chemical. Possible mechanisms affecting the modulation of gap junctional communication by these chemicals are discussed.Abbreviations: Hypoxanthine guanine, phosphoribosyltranferase, HG-PRT; 6-thioguanine, 6-TG.On leave from: Beijing Municipal Research Institute of Environmental Protection, Beijing, People's Republic of China     

TRANSPROTECTION OF SILYL ETHERS OF NUCLEOSIDES IN FeCl3 BASED IONIC LIQUIDS

Ionic liquid mediated deprotection of tert-butyldimethyl silyl (TBDMS) ethers derived from various primary and secondary alcohols have been studied and the reaction conditions optimized. Deprotection of the silyl ethers in FeCl3 based ionic liquids in presence of acetic anhydride yielded the acetate esters of the corresponding alcohols in good yields. The transprotection methodology was extended to the silyl ethers of nucleosides to yield the corresponding acetylated products.     

Enzymatic synthesis of the acrylic esters: a comparative study

Various acrylic esters were synthesized by Candida cylindracea lipase (CCL) catalysed transesterification with different alcohols. A comparative study was carried out using 2,3-butanedione mono-oxime acrylate and vinyl acrylate as acylating agents. The rate of conversion was faster when oxime acrylate was used as acylating agent as compared to vinyl acrylate. Effect of solvents on the rate of conversion was studied and diisopropyl ether (DIPE) was proved to be a better solvent as compared to CHCl₃ and THF. The effect of various structural aspects of the substrates on the rate of conversion was studied. Among the linear alcohols studied, ease of conversion was found to be in the order of n-octanol>n-hexanol>n-butanol. Up to 80% conversion was achieved in the case of cyclohexyl methanol.     

Kinetic and Mechanistic Studies of a Novel Carbonyl Reductase Isolated from Candida Parapsilosis

The novel carbonyl reductase from Candida parapsilosis (CPCR) exhibits a very broad substrate specificity, accepting primary and secondary alcohols, aldehydes, ketoacetals, aliphatic and aromatic ketones, cyclic ketones, diketones, halogenated ketones, keto esters and halogenated keto esters of variable chain length as substrates. Based on the kinetic constants of a variety of different substrates a hypothetical model of the substrate-binding site is proposed. The small alkyl side chain of the carbonyl compound is bound to a small pocket of the binding site, while the large alkyl group is orientated towards the large hydrophobic pocket. This model and the kinetic data enables the prediction of whether a substrate of interest may be reduced by the CPCR. Product inhibition studies are reported which show that the kinetic mechanism of the CPCR is Ordered Bi-Bi, with the nucleotide adding to free enzyme before the other substrate. Alcohols and/or ketones are adsorbed at sites other than the active site and alter the catalytic properties of the enzyme. The enzyme transfers the pro-R hydride of NADH to the re face of the carbonyl compounds yielding (S) alcohols.     

Solvent as a competitive inhibitor for Candida antarctica lipase B

In enzyme-catalyzed reactions, the choice of solvent often has a marked effect on the reaction outcome. In this paper, it is shown that solvent effects could be explained by the ability of the solvent to act as a competitive inhibitor to the substrate. Experimentally, the effect of six solvents, 2-pentanone, 3-pentanone, 2-methyl-2-pentanol, 3-methyl-3-pentanol, 2-methylpentane and 3-methylpentane, was studied in a solid/gas reactor. As a model reaction, the CALB-catalyzed transacylation between methyl propanoate and 1-propanol, was studied. It was shown that both ketones inhibited the enzyme activity whereas the tertiary alcohols and the hydrocarbons did not. Alcohol inhibition constants, K(i)(I) were changed to "K(i)", determined in presence of 2-pentanone, 3-pentanone, and 3-methyl-3-pentanol, confirmed the marked inhibitory character of the ketones and an absence of inhibition of 3-methyl-3-pentanol. The molecular modeling study was performed on three solvents, 2-pentanone, 2-methyl-2-pentanol and 2-methyl pentane. It showed a clear inhibitory effect for the ketone and the tertiary alcohol, but no effect for the hydrocarbon. No change in enzyme conformation was seen during the simulations. The study led to the conclusion that the effect of added organic component on lipase catalyzed transacylation could be explained by the competitive inhibitory character of solvents towards the first binding substrate methyl propanoate.     

Ester synthesis from trimethylammonium alcohols in dry organic media catalyzed by immobilized Candida antarctica lipase B

Twenty-one different organic solvents were assayed as possible reaction media for the synthesis of butyryl esters from trimethylammonium alcohols in dry conditions catalyzed by immobilized Candida antarctica lipase B. The reactions were carried out following a transesterification kinetic approach, using choline and L-carnitine as primary and secondary trimethylammonium alcohols, respectively, and vinyl butyrate as acyl donor. The synthetic activity of the enzyme was strictly dependent on the water content, the position of the hydroxyl group in the trimethylammonium molecule, and the Log P parameter of the assayed solvent. Anhydrous conditions and a high excess of vinyl butyrate over L-carnitine were necessary to synthesize butyryl-L-carnitine. The synthetic reaction rates of butyryl choline were practically 100-fold those of butyryl-L-carnitine with all the assayed solvents. In both cases, the synthetic activity of the enzyme was dependent on the hydrophobicity of the solvent, with the optimal reaction media showing a Log P parameter of between -0.5 and 0.5. In all cases, 2-methyl-2-propanol and 2-methyl-2-butanol were shown to be the best solvents for both their high synthetic activity and negligible loss of enzyme activity after 6 days.     

Stimulation of tarsal receptors of the blowfly by aliphatic aldehydes and ketones

Rejection of eight aldehydes, eight ketones, five secondary alcohols, and 3-pentanol has been studied in the blowfly Phormia regina Meigen. The data agree with results previously reported for normal alcohols and several series of glycols in showing a logarithmic increase in stimulating effect with increasing chain length. The order of increasing effectiveness among the different species of compounds thus far investigated is the following: polyglycols, diols, secondary alcohols, iso-alcohols, normal alcohols, ketones, iso-aldehydes, normal aldehydes. Curves relating the logarithms of threshold concentration to the logarithms of chain length for diols, alcohols, aldehydes, and ketones show inflections in the 3 to 6 carbon range. Above and below the region of inflection the curves are nearly rectilinear. The slopes for the upper limbs (smaller molecules) are of the order of -2; for the lower limbs, about -10. Comparisons of the threshold data with numerical values for molecular weights, molecular areas and volumes, oil-water distribution coefficients, activity coefficients, standard free energies, vapor pressures, boiling points, melting points, dipole moments, dielectric constants, and degree of association are discussed briefly, and it is concluded that none of the comparisons serves to bring the data from the several series and from the two portions of each series into a single homogeneous system. A qualitative comparison with water solubilities shows fewer discrepancies. It is suggested that the existence of a combination of aqueous and lipoid phases at the receptor surface would fit best with what is presently known about the relationship between chemical structure and stimulating effect in contact chemoreception. In this hypothesis the smaller and more highly water-soluble compounds are envisaged as gaining access to the receptors partly through the aqueous phase, the larger molecules predominantly through the lipoid phase.     

Biosynthesis of plant-derived flavor compounds

Plants have the capacity to synthesize, accumulate and emit volatiles that may act as aroma and flavor molecules due to interactions with human receptors. These low-molecular-weight substances derived from the fatty acid, amino acid and carbohydrate pools constitute a heterogenous group of molecules with saturated and unsaturated, straight-chain, branched-chain and cyclic structures bearing various functional groups (e.g. alcohols, aldehydes, ketones, esters and ethers) and also nitrogen and sulfur. They are commercially important for the food, pharmaceutical, agricultural and chemical industries as flavorants, drugs, pesticides and industrial feedstocks. Due to the low abundance of the volatiles in their plant sources, many of the natural products had been replaced by their synthetic analogues by the end of the last century. However, the foreseeable shortage of the crude oil that is the source for many of the artifical flavors and fragrances has prompted recent interest in understanding the formation of these compounds and engineering their biosynthesis. Although many of the volatile constituents of flavors and aromas have been identified, many of the enzymes and genes involved in their biosynthesis are still not known. However, modification of flavor by genetic engineering is dependent on the knowledge and availability of genes that encode enzymes of key reactions that influence or divert the biosynthetic pathways of plant-derived volatiles. Major progress has resulted from the use of molecular and biochemical techniques, and a large number of genes encoding enzymes of volatile biosynthesis have recently been reported.     

Solvent effects on the stability of nifuroxazide complexes with cobalt(II), nickel(II) and copper(II) in alcohols

A spectrophotometric study of the complexation of nifuroxazide with cobalt(II), nickel(II) and copper(II) was carried out in different alcohols. The formation of a complex in each case is reported and their stability constants have been calculated. For a given solvent, the stability of the complexes increases from cobalt to copper. In the case of copper(II), the stability varies as an inverse function of the dielectric constant of the solvent. A possible structure of the complex is proposed.     

Asymmetric synthesis with immobilized yeast in organic solvents: equilibrium conversion and effect of reactant partitioning on whole cell biocatalysis

A newly isolated strain of the yeast Saccharomyces cerevisiae is investigated for the biocatalytic reduction of ketones and the oxidation of alcohols in organic solvents. The yeast cells are immobilized by entrapment within calcium alginate beads and are found to possess the ability to stereoselectively reduce prochiral ketones and oxidize chiral alcohols to equilibrium conversions. The effect of reactant partitioning on the initial rate of the reactions is also investigated. The observed initial rates are found to vary inversely with reactant partitioning between the organic solvent and the biocatalyst beads. A kinetic model is developed to describe the initial reaction rate of hexanone reduction as a function of substrate concentration within the alginate beads.     

Solvent effects on the conformation and far UV CD spectra of gramicidin

Solvent effects on the far-uv CD spectra of the polypeptide gramicidin have been studied systematically in a series of alcohols of increasing chain length, ranging from methanol to dodecanol. The effects observed are of two types: primary, involving a change in the equilibrium mixture of conformers present, and secondary, involving a shift in the spectral peak positions as a function of solvent polarizability. To quantitate the primary effect, the ratio of the individual conformers present was estimated by deconvolution of the spectra into their component species. For short chain length alcohols, both parallel and antiparallel double helices are found in considerable abundance. As the solvent chain length is increased and its polarity is decreased, the left-handed antiparallel double helical species is favored. For all alcohols with chain lengths of four or more carbon atoms, the ratio of the conformers present remains relatively constant. To quantitatively examine the secondary effect, the magnitudes of the spectral shifts on the dominant conformer (species 3) have been correlated with the dielectric constants and refractive indices of the solvents, thereby indicating what underlying physical properties are responsible for these shifts. This work thus demonstrates that for gramicidin, a flexible polypeptide, the solvent effects on the CD spectra can be resolved into two types: changes due to the mixture of conformers present and shifts in the spectral characteristics. Both effects need to be considered when interpreting CD spectra in terms of secondary structure for this and other polypeptides in nonaqueous solutions.     

An estimation of the equivalent solution dielectric constant in the active-site cavity of metalloenzymes. Dependence of carboxylate-metal-ion complex stabilities on the polarity of mixed aqueous/organic solvents

The stability constants of the 1:1 complexes between Cu2+ and Zn2+ with formate, acetate and several phenylalkanecarboxylates, i.e. C6H5-(CH2)n-COO- with n = 0 to 5, are summarized for water, 50% aqueous ethanol and 50% aqueous dioxane (I = 0.1 M; 25 degrees C): Complex stability depends upon carboxylate group basicity. The influence of varying amounts of ethanol or dioxane (up to 90%) on the stability of the Cu2+ and Zn2+ (M2+) complexes with formate and acetate (CA) was measured by potentiometric pH titrations. The values for pKHH(CA) and log KMM(CA) increase, as expected, with increasing amounts of the organic solvents, i.e. with decreasing solvent polarity. The changes in the equilibrium constants are also evaluated with regard to the mole fractions of the organic solvents and the corresponding dielectric constants. These results may be used to estimate for low dielectric cavities in proteins the equivalent solution dielectric constant on the basis of enhanced carboxylate basicity or metal ion binding capability (method 1). Furthermore, the measured stability constants are used for comparisons of the coordination tendency of carboxylate ligands towards zinc(II)-metalloenzymes (method 2); in this way the equivalent solution dielectric constants in the active-site cavities of bovine carbonic anhydrase and carboxypeptidase A are estimated: the values are of the order of 35 and 70, respectively. This method seems to be generally applicable to metalloproteins.