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Scanning calorimetry measurements of different amounts of chymotrypsin in water alone gave a temperature of denaturation (Td) value of 54°C. However, when high‐molecular‐weight poly(ethylene glycol) was added to aqueous solutions of chymotrypsin, the thermostability of the enzyme was enhanced. For example, the addition of 20% (w/w) of poly(ethylene glycol) of molecular weight of 100,000 increased
Rhizopus arrhizus lipase immobilized on celite was used to prepare isomerically pure 2-monoglycerides by alcoholysis of triglycerides in organic media. Reaction parameters such as choice of solvent, choice of alcohol, and alcohol concentration were studied. When 12.5 mM tripalmitin was used as substrate, methyl-tert-butyl ether was the best solvent for alcoholysis at water activity 0.11. Ethanol g
A technique of continuous water activity control was used to examine the effects of water activity on enzyme catalysis in organic media. Esterification catalyzed by Rhizopus arrhizus lipase was preferably carried out at a water activity of 0.33, which resulted in both maximal initial reaction rate and a high yield. When Pseudomonas lipase was used as catalyst it was beneficial to start the reactio
A recent method for exposing enzymes to organic solvents is reviewed. By complex formation between the enzyme and polymers that per se are soluble in organic solvents it is possible to disperse the enzyme in the organic medium in such a way that an optically transparent (in the visible region) solution is obtained. After reaction, the separation of the enzyme from the organic medium can be obtaine
Mixing solutions of polymers dissolved in chloroform resulted in turbid solutions that parted into two separate phases upon standing. Each phase consisted primarily of one of the two polymers and contained only small amounts of the other. An enzyme (α‐chymotrypsin) added to the two‐phase system partitioned preferentially to one of the phases; this was observed with native enzyme and with enzyme as
The progress of enzymatic peptide synthesis catalyzed by α-chymotrypsin and subtilisin from Bacillus subtilis strain 72 (subtilisin 72) in low-water systems was studied. The initial reaction mixture consisted of the solvent, the acyl-group donor (MalAlaAlaPheOMe or ZAlaAlaPheOMe, Mal, maleyl, Z, benzyloxycarbonyl), the nucleophile XaaNH2 (Xaa = Phe, Leu or Ala), and the enzyme adsorbed on porous s
The use of β-glucosidase for synthesizing octyl-β-glucoside was studied. Almond β-glucosidase immobilized on XAD-4, glucose, and octanol were mixed at controlled water activity. A water activity of at least 0.67 was needed for synthesis of octyl-β-glucoside, and the reaction rate increased with increasing water activity. The final yield decreased with increasing water activity. The best results we
Octanoylglucose was synthesized from insoluble glucose and octanoic acid in acetonitrile, using lipase from Candida antarctica as catalyst. The initial concentration of octanoic acid was optimized to give complete conversion of glucose to monoester and avoid diester formation. The acylation occurred exclusively at the primary hydroxyl group on the glucose ring.
Pepsin‐catalyzed synthesis of protected peptides was studied in two‐phase systems containing up to 50% (by volume) of aqueous phase. A methodological study was carried out to determine the optimum conditions for the synthesis of the model protected peptide Z‐Phe‐Phe‐OMe. Several parameters such as concentrations of carboxylic and amino components, pH of the aqueous phase, ratio of organic to aqueo
Lipase from Candida rugosa immobilized on Celite was employed as the biocatalyst in order to examine the effect of the reaction medium upon enzymic activity and selectivity. As the model reaction, transesterification between tributyrin and pentan‐2‐ol in iso‐octane (2,2,4‐trimethylpentane) was chosen. A small amount of water (0.05%, v/v) was added to the reaction medium. Enhanced transesterificati
αChymotrypsin was modified with cyanuric chloride activated monomethoxypolyethylene glycol (MPEG) with molecular weights 1900 and 5000. Using the higher molecular weight MPEG a product that was soluble in benzene at moderate levels of modification was obtained, whereas with MPEG 1900 almost all the enzyme's amino groups had to be modified for dissolving the conjugate. The catalytic activity decrea
Phosphatidylcholines composed of a hexadecyl chain in the 2-position and a hexyl or octyl chain in the l-position (C6C16PC or C8C16PC) were prepared from dipalmitoylphosphatidylcholine by lipase-catalyzed transesterification; the aqueous phase properties of the products were examined. In the C8C16PC-water system, a lamellar liquid-crystalline phase was dominant. Like all long-chain phosphatidylcho
The composition and content of the gastric phospholipids were followed during development and healing of indometha-cin-induced chronic, antral ulcers in rats. The individual phospholipids were identified by thin-layer chromatography and quantitatively estimated by spectrophotometric analysis of phosphate. No changes were found in phospholipid composition and content after a 24-hour fast or during
Enzymes deposited on solid support usually show good stability when operated in organic solvents. Decreased stability of the enzyme preparations was noticed when low enzyme loadings were used (e.g., with Celite as support; less than 1 mg enzyme/g). It was possible to avoid the activity loss by the addition of an additive which protects the enzyme during the immobilization. Proteins (such as albumi
α‐Chymotrypsin‐catalyzed acyl tranfer was studied using three acyl‐group donors (Mal‐l‐Ala‐l‐Ala‐l‐PheOMe, Bz‐l‐TyrOEt and Ac‐l‐TrpOEt; Mal, maleyl; Bz, benzoyl; OMe, methyl ester; OEt, ethyl ester) and a series of amino‐acid amides. Most of the reactions studied can be described by the simplest kinetic model without the nucleophile binding to the acyl‐enzyme. The α‐chymotrypsin‐catalyzed transfer
Horse liver alcohol dehydrogenase and α-chymotrypsin were deposited on a porous support material, Celite. After equilibration at a well-defined water activity, the catalytic activity was measured with diisopropyl ether as reaction medium. The effects of the presence of polyols and simple saccharides in the preparations were investigated. The additives caused a considerable increase in the amount o
The influence of eight different N-terminal protecting groups (For, Ac, Boc, Fmoc, Mal, Pheac, Aloc and Z) on the α-chymotrypsin-catalyzed synthesis of the dipeptide derivative X-Phe-Leu-NH2 in organic media was studied. Groups such as Ac, For, Boc, Z, Mal, Pheac and Alloc always rendered good peptide yields (92% to 99%) either in acetonitrile or in ethyl acetate. Good correlations were found betw
This paper describes a newly developed technique to adjust and control the water activity in enzymatic reactions in organic media. A saturated salt solution of known water activity is circulated inside a silicone tube, submerged into the reaction medium. The circulating solution can both absorb and release water. Water activity control during lipase catalyzed esterification was demonstrated with d
The reaction kinetics of αchymotrypsin (EC 3.4.21.1.) catalyzed esterification of N-protected phenylalanine with ethanol were studied. The enzyme was deposited on Chromosorb and reactions were performed mainly in water-saturated mixtures of ethyl acetate and heptane, but also other media were used, such as mixtures of ethyl acetate and acetonitrile. The hydrophobicity of the substrate was varied b
