Preparation of some immobilized linked enzyme systems and their use in the automated determination of disaccharides

A three-cascaded-enzymes biosensor to determine lactose concentration in raw milk

The increasing demand for on-line measurement of milk composition directs science and industry to search for practical solutions, and biosensors may be a possibility. The specific objective of this work was to develop an electrochemical biosensor to determine lactose concentration in fresh raw milk. The sensor is based on serial reactions of three enzymes--beta-galactosidase, glucose oxidase, and horseradish peroxidase--immobilized on a glassy carbon electrode. The sequential enzymatic reactions increase the selectivity and sensitivity of the sensor. The sensor requires dilution of the raw milk and the addition of 5-aminosalicylic acid. Lactose concentrations in raw milk measured by the sensor were in good agreement with those measured by a reference laboratory using infrared technology. The results were obtained in milk samples that varied in fat and protein composition. From the results, we conclude that an electrochemical biosensor for determination of lactose concentration in fresh raw milk can be developed, and that the biosensor presented in this study maintained the qualities required for further development into an online sensor in the milking parlor.

Entrapment of enzymes using organo-functionalized polysiloxane copolymers

The present study expands previous work [(1984) Biochim. Biophys. Acta. 797, 343-347] by showing that organo-functionalized polysiloxane copolymers could entrap two of the most frequently immobilized enzymes, i.e. urease and invertase with retention of biological activity. Urease was solidly entrapped in the polymer formed from a 1:3 mixture of 3-aminopropyltriethoxysilane and tetraethylorthosilicate. The entrapment yield and the activity of the entrapped enzyme are significantly greater than with other techniques reported to date. Significantly, the entrapped enzyme possessed greater activity than its solution counterpart (36% at higher amounts of enzyme entrapped). The entrapment process also rendered the enzyme more stable toward pH and temperature, and less susceptible toward the action of urea at high concentrations. In addition, the entrapment process significantly increased the stability, both operational and storage, of the urease enzyme. When invertase was entrapped in the same copolymer, it retained two thirds of its solution activity, but the entrapment yield was lower than that of urease. Results obtained during this study also suggested that the protein may be influencing polymer development in these systems and that the resultant polymer in turn may be affecting the enzyme's activity (see following paper for further discussion).

A versatile solid support system for oligodeoxynucleotide probe-based hybridization assays

A procedure for immobilization of well-defined quantities of oligodeoxyribonucleotides (ODNs) to a versatile nylon support is described. The solid support, a nylon-6/6 bead, is covalently coated with poly(ethyleneimine) to provide a reactive spacer-arm for attachment of ODNs. 5'-Aminohexyl-tailed ODNs are selectively activated using 2,4,6-trichloro-1,3,5-triazine (cyanuric chloride) and then covalently attached to the bead via the triazine moiety. The modified nylon support has a low level of binding of nonspecific nucleic acid and efficiently captures both RNA and DNA targets.

Flow injection analysis of lactose using covalently immobilized beta-galactosidase, mutarotase, and glucose oxidase/peroxidase on a 2-fluoro-1-methylpyridinium salt-activated Fractogel support

Milk samples were analyzed for their lactose content using flow injection analysis and incorporating immobilized beta-galactosidase or beta-galactosidase/mutarotase and glucose oxidase/peroxidase bioreactors. These enzymes were immobilized, under mild conditions, on to a 2-fluoro-1-methylpyridinium salt-activated Fractogel support. The use of a phosphate buffer (0.15 M) was found to facilitate the rapid mutarotation of alpha-D-glucose and hence could obviate the need for the more expensive mutarotase. The chromogenic agents of choice for monitoring the reaction were 3-methyl-2-benzothiazolinone hydrazone and 3-dimethylaminobenzoic acid. Linearity was observed over the concentration range 16-160 micrograms/ml using lactose standards (r = 0.996). Between 30 and 40 milk samples/h can be analyzed. Comparisons are made with existing HPLC and alkaline methylamine methods for a range of milk matrices. The FIA method consistently gives the lowest standard deviations and coefficient of variation for the various milk matrices analyzed.

Keratin and polyamide-coated inorganic matrices as supports for glucoamylase immobilization

Previously solubilized feather keratin and polyamide were used for coating sand, glass beads and silica gel. These new seven supports were employed for comparative studies on pure glucoamylase / EC 3.2.1.3 / immobilization. The immobilization yield of glucoamylase on keratin and polyamide coated supports was comparable with conventional matrices used earlier. The highest activity per 1 g of support was shown by the enzyme bound to polyamide-coated CPG, and the bests operational stability by the enzyme immobilized on polyamide-coated CPG with keratin subsequently deposited on it.

Flow kinetics of yeast alcohol dehydrogenase attached to nylon tubing

Yeast alcohol dehydrogenase (alcohol:NAD+ oxidoreductase, EC 1.1.1.1) was attached covalently to the inner surface of nylon tubing, and the immobilized enzyme retained its activity over a period of months. A study was made of the flow kinetics for the reaction between ethanol and NAD. With the ethanol held at saturating concentrations there was partial diffusion control, the extent decreasing with increasing flow rate and increasing NAD concentration. With the NAD at saturating concentrations there was no appreciable diffusion control. The apparent Michaelis constants varied with flow rate vf, being linear in vf-1/3, and extrapolation to infinite flow rate (vf-1/3 = 0) gave the intrinsic Michaelis constants. The inhibition by products was also studied. The results for both NADH and acetaldehyde showed mixed competitive and non-competitive inhibition, with a preponderance of the former. Acetaldehyde is the stronger inhibitor, and this is consistent with the lack of dissusion control with variable ethanol. Inhibition by acetaldehyde is not affected by flow rate, but inhibition by NADH is affected, presumably because of the greater degree of diffusion control with variable NAD.

Hydrolysis of galactose from glycolipids and glycoprotein by young rat brain beta-galactosidases immobilized to Sepharose 4B

An extract of glycosidic enzymes from young rat brain was immobilized to cyanogen bromide-activated Sepharose 4B. Most glycosidases retained approximately 10--25% of their activities after immobilization. Immobilized beta-galactosidases were used repeatedly without detectable loss of enzyme activity in the hydrolysis of p-nitrophenyl-beta-D-galactopyranoside. In addition to the synthetic substrate, the immobilized rat brain beta-galactosidases could also hydrolyze galactose from lactose, galactosylcerebroside, asialofetuin, and GM1-ganglioside. The hydrolysis of GM1- to GM2-ganglioside was confirmed on TLC.

Immobilization of beta-galactosidase and other enzymes onto p-amino-carbanilated cellulose derivatives

beta-Galactosidase and other enzymes were immobilized on p-amino-carbanilated derivatives of cellulose and methylol cellulose using the diazo method and through glutaraldehyde. The optimum conditions for coupling cellulose tri-(p-amino-carbanilate) (CTAC) to beta-galactosidase were established. The diazo coupling method with CTAC gave greater activity than with glutaraldehyde when coupled to beta-galactosidase (Escherichia coli). The stability of the CTAC-beta--galactosidase system was examined. The disubstituted p-amino-carbanilate derivative (CDAC) gave a lower activity, whereas the methylol analog (MCTAC) gave slightly greater activity. The CTAC was also used to immobilize glucose oxidase, trypsin, pepsin, and papain.

Hydrolysis of D-galactosides in an open tubular lactase reactor

Lactase (beta-galactosidase) was attached to the inner surface of nylon tubing. Tubes of various lengths were used to bring about the hydrolysis of o-nitrophenyl-beta-D-galactoside and of lactose in skim milk. The results with the former substrate were analyzed in the light of a theoretical treatment of Kobayashi and Laidler (Biotechnol. Bioeng., 16, 99, 1974), with the conclusion that the reaction is intermediate between diffusion-free and completely diffusion-controlled behavior. The results with skim milk show that with a single 46 m tube and continuous circulation, 90% of the lactose is removed within 20 hr. A battery of ten such tubes, with single passage, at a flow rate of 2 cm/sec, would remove more than 99% of the lactose in less than 40 min.

Immobilized glutamate oxaloacetate transaminase. Steady state kinetic analysis and stability studies

1. Glutamate oxaloacetate transaminase (L-aspartate: 2-oxoglutarate aminotransferase, EC 2.6.1.1) was immobilized on amino ethyl cellulose using the bifunctional reagent diethyl adipimidate. 2. The steady state kinetic analysis was performed for the particulate and the free enzyme, and the Michaelis constants measured for the amino ethyl cellulose derivative were not greatly different from those measured for the free glutamate oxaloacetate transaminase, while the latter were in good agreement with values in the literature. 3. The amino ethyl cellulose-glutamate oxaloacetate transaminase was slightly more stable than the free enzyme at 65 degrees C, but was stabilised less by polyethylene glycol than the free enzyme.

Immobilized electric eel acetylcholinesterasemii. II. Flow kinetics of acetylcholinesterase chemically attached to nylon tubing

Acetylcholinesterase has been attached covalently to the inner surface of nylon tubing. An experimental study has been carried out on the flow kinetics; solutions of acetylthiocholine at various concentrations were passed through tubing at various flow rates, and measurements made of the rates of formation of product. The results were analyzed in the light of the theoretical treatment of Kobayashi and Laidler, four different methods of analysis being employed. It is found that at lower substrate concentrations and flow rates the reactions are largely diffusion controlled. The Km(app) values are substantially higher than the Km value for diffusion-free conditions, but approach it as the flow rate is increased, when the diffusion layer becomes less important. The results are entirely consistent with the Kobayaski-Laidler theory, and provide guidelines for the design of open tubular heterogeneous enzyme reactors, both for industrial and analytic purposes.