Enzymes Part 3 Flashcards
Certain enzymes have __________ on their active sites, and these _____________ must be in suitable form (acid or base) to function.
ionic groups, ionic groups
________________ result in changes in the ionic form of the active site and changes in the activity of the enzyme and hence the reaction rate.
Variations in the pH of the medium
___________ may also alter the three-dimensional shape of the enzymes. For these reasons, enzymes are only active over a certain pH range.
Changes in pH
The _______________ may affect the maximum reaction rate, the constant, and the stability of the enzyme.
pH of the medium
____________ of enzymes requires a knowledge of the active site characteristics of enzymes, which are very difficult to obtain.
Theoretical prediction of the pH optimum
____________ for an enzyme is usually determined experimentally.
The pH optimum
The descending part of the graph of the figure is known as _________________.
temperature inactivation or thermal degradation
_________ are often used to attack large, insoluble substrates such as wood chips (in bio pulping for paper manufacture) or cellulosic residues from agriculture (cornstalks).
Enzymes
In these cases, access to the ____________ on these biopolymers by enzymes is often limited by enzyme diffusion. The number of potential reactive sites exceeds the number of the enzyme molecules.
reaction rate
This situation is opposite that of the typical situation with___________, where access to the enzyme’s active site limits the reaction.
soluble substrates
The restriction of enzyme mobility in a fixed space is known as ________________.
enzyme immobilization
Immobilization of enzymes provides important advantages, such as ________________________ and may provide a better environment for enzyme activity.
- enzyme reutilization and
- elimination of enzyme recovery and
- purification processes,
Since enzymes are expensive, _________ is critical for many processes.
catalyst reuse
Since some of the ____________ are membrane bound, immobilized enzymes provide a model system to mimic and understand the action of some membrane-bound intracellular enzymes.
intracellular enzymes
___________ is usually improved, and effluent handling problems are minimized by immobilization.
Product purity
Methods of immobilization entrapment:
- Entrapment
- Matrix entrapment and membrane entrapment,
- Matrices
____________ is the physical enclosure of enzymes in a small space.
Entrapment
_____________, including microencapsulation, are two major methods of entrapment.
Matrix entrapment and membrane entrapment
___________ used for enzyme immobilization are usually polymeric materials such as Ca-alginate, agar, k-carrageenin, polyacrylamide, and collagen.
Matrices
However, some _________ such as activated carbon, porous ceramic, and diatomaceous earth can be also used for this purpose.
solid matrices
The ___________ can be a particle, a membrane, or a fiber.
matrix
When _______________ in a polymer matrix, enzyme solution is mixed with polymer solution before polymerization takes place.
immobilizing
_________________ is either extruded or a template is used to shape the particles from a liquid polymer-enzyme mixture. Entrapment and surface attachment may be used in combination in some cases.
Polymerized gel-containing enzyme
__________________ is possible; for example, hollow fiber units have been entrapping an enzyme solution between thin, semipermeable membranes.
Membrane entrapment of enzymes
_____________ of nylon, cellulose, polysulfone, and polyacrylate are commonly used.
Membranes
Configurations, other than _____________ are possible, but in all cases a semipermeable membrane is used to retain high molecular weight compounds (enzyme), while allowing small molecular weight compounds (substrate or products) access to the enzyme.
hollow fibers
A special form of membrane entrapment is ______________. In this technique, microscopic hollow spheres are formed. The spheres containing the enzyme solution, while the sphere is enclosed within a porous membrane. The membrane can be polymeric or an enriched interfacial phase formed around a micro drop.
microencapsulation
Despite the aforementioned advantages, ____________ may have its inherent problems such as enzyme leakage into solution, significant diffusional limitations, reduced enzyme activity and stability, and lack of control of microenvironmental conditions.
enzyme entrapment
_________________ can be overcome by reducing the MW cutoff of membranes or the pore size of solid matrices.
Enzyme leakage
______________ can be eliminated by reducing the particle size of matrices and/or capsules.
Diffusional limitations
_______________ are due to unfavorable microenvironmental conditions, which are difficult to control. However, by using different matrices and chemical ingredients, by changing processing conditions, and by reducing particle or capsule size, more favorable microenvironmental conditions can be obtained.
Reduced enzyme activity and stability
________________ is usually less significant in microcapsules as compared to gel beads.
Diffusion barrier
The two major types of immobilizations of enzymes on the surfaces of support materials are _______________.
adsorption and covalent binding.
_________ is the attachment of enzymes on the surfaces of support particles by weak physical forces, such as van der Waals or dispersion forces.
Adsorption
The___________________ is usually unaffected, and nearly full activity is retained upon adsorption.
active site of the adsorbed enzyme
However, ________________ is a common problem, especially in the presence of strong hydrodynamic forces, since binding forces are weak.
desorption of enzymes
___________________ may be stabilized by cross-linking with glutaraldehyde.
Adsorption of enzymes
__________________ treatment can denature some proteins
Glutaraldehyde
____________________ used for enzyme adsorption can be inorganic materials such as alumina, silica, porous glass, ceramics, diatomaceous earth, clay, bentonite, or organic materials such as cellulose (CMC, DEAE-cellulose), starch, activated carbon, and ion exchange resins, such as Amberlite, Sephadex, and Dowex.
Support materials
The surfaces of the support materials may need to be ____________ for effective immobilization.
pretreated (chemically or physically)
_________________ is the retention of enzymes on support surfaces by covalent bond formation.
Covalent binding
Enzyme molecules bind to support material via certain functional groups, such as _____________.
amino, carboxyl, hydroxyl, and sulfhydryl groups
These ___________ must not be in the active sites.
functional groups
One common trick is to ______________ by flooding the enzyme solution with a competitive inhibitor prior to covalent binding
block the active site
______________ are usually activated by using chemical reagents, such as cyanogen bromide, carbodiimide, and glutaraldehyde.
Functional groups on support material
Binding groups on the protein molecule are usually side groups ________________.
(R) or the amino or carboxyl groups of the polypeptide chain.
Cross-linking can be achieved in several different ways:
- enzymes can be crosslinked with glutaraldehyde to form an insoluble aggregate,
- adsorbed enzymes may be cross-linked, or
- cross-linking may take place following the impregnation of porous support material with enzyme solution.
The_____________ molecules with each other using agents such as glutaraldehyde, bis-diazo benzidine, and 2,2-disulfonic acid is another method of enzyme immobilization.
cross-linking of enzyme
____________ may cause significant changes in the active site of enzymes, and also severe diffusion limitations may result.
Cross-linking
The ___________ support material and immobilization method vary depending on the enzyme and particular application.
most suitable
Two major criteria used in the selection of support material are
(1.) the binding capacity of the support material, which is a function of charge density, functional groups, porosity, and hydrophobicity of the support surface, and
(2.) stability and retention of enzymatic activity, which is a function of functional groups on support material and microenvironmental conditions
If____________ causes some conformational changes on the enzyme, or if reactive groups on the active site of the enzyme are involve in binding, a loss in enzyme activity can take place upon immobilization.
immobilization
Usually, ___________ results in a loss of enzyme activity and stability.
immobilization
However, in some cases, immobilization may cause an increase in enzyme activity and stability due to more ______________. Because enzymes often have more than one functional site that can bind the surface, an immobilized enzyme preparation may be very heterogeneous.
favorable microenvironmental conditions
Even when____________ does not alter enzyme structure, some enzyme can be bound with the active site oriented away from the substrate solution and toward the support surface, decreasing the access of the substrate to the enzyme.
binding
_________________ varies with the method used.
Retention of activity
Among various enzymes produced at large scale __________ (subtilisin, rennet), ____________ (pectinase, lipase, lactase), ___________ (glucose isomerase), and _____________(glucose oxidase). These enzymes are produced using overproducing strains of certain organisms.
- proteases
- hydrolases
- isomerases
- oxidases
____________ of an enzyme from an organism require disruption of cells, removal of cell debris and nucleic acids, precipitation of proteins, ultrafiltration of the desired enzyme, chromatographic separations (optional), crystallization, and drying.
Separation and purification
The process scheme varies depending on whether the enzyme is ________________.
intracellular or extracellular
In some cases, it may be more advantageous to use _________ with the desired enzyme activity in immobilized form. This approach eliminates costly enzyme separation and purification steps and is therefore economically more feasible.
inactive (dead or resting) cells
The first step in the large-scale production of enzymes is to ___________producing the desired enzyme.
cultivate the organisms
_________ can be regulated and fermentation conditions can be optimized for overproduction of the enzyme.
Enzyme production
_________ are produced by using overproducing strains of Bacillus, Aspergillus, Rhizopus, and Mucor
Proteases
____________________ are produced by Aspergillus niger;
Pectinases
_________ are produced by certain strains of yeast and fungi.
Lipases
________________ is produced by Flavobacterium arborescens or Bacillus coagulans.
Glucose isomerase
After the cultivation step, cells are __________________ usually by filtration or sometimes by centrifugation. Depending on the intracellular or extracellular nature of the enzyme.
separated from the media
Either the _______________is further processed to separate and purify the enzyme.
cells or the fermentation broth
The recovery of _____________ is more complicated and involves the disruption of cells and removal of cell debris and nucleic acids.
intracellular enzymes
In some cases, enzyme may be __________________, which required processing of both broth and cells.
both intracellular and extracellular
_________________may be released by increasing the permeability of cell membrane. Certain salts such as calcium chloride and other chemicals such as dimethyl sulfoxide (DMSO) and pH shift may be used for this purpose.
Intracellular enzymes
If __________is not complete, then cell disruption may be essential.
enzyme release
____________ hydrolyze proteins into smaller peptide units and constitute a large and industrially important group of enzymes.
Proteases
_____________ constitute about 60% of the total enzyme market. Industrial proteases are obtained from bacteria (Bacillus), molds (Aspergillus, Rhizopus, and Mucor), animal pancreas, and plants.
Proteases
Most of the industrial proteases are __________
Endo proteases
_______________ are used in food processing, such as cheese making (rennet), baking, meat tenderization (papain, trypsin), and brewing (trypsin, pepsin); in detergents for the hydrolysis of protein stains (subtilisin Carlsberg); and in tanning and the medical treatment for wounds.
Proteases
____________ are produced mainly by A. niger.
Pectinases
The major components in pectinases are ______________, _____________, and _____________.
- pectin esterase,
- polygalacturonase, and
- polymethylgalacturonatelyase.
_______________ are used in fruit juice processing and wine making to increase juice yield, reduce viscosity, and clear the juice.
Pectinases
_____________ hydrolyze lipids into fatty acids and glycerol and are produced from animal pancreas, some molds, and yeast.
Lipases
____________ may be used to hydrolyze oils for soap manufacture and to hydrolyze the lipid-fat compounds present in waste-water streams.
Lipases
____________________ may be catalyzed by lipases. Lipases may also be used in the cheese and butter industry to impart flavor as a result of the hydrolysis of fats.
Interesterification of oils and fats
_________ containing detergents are an important application of lipases.
Lipase
___________ are used for the hydrolysis of starch and are produced by many different organisms including A. niger and B. subtilis.
Amylases
Three major types of amylases are ______________, _____________, and _____________.
- a-amylase,
- b-amylase, and ‘
- glucoamylase
__________ breaks a -1,4 glycosidic bonds randomly on the amylose chain and solubilizes amylose. For this reason, a-amylase is known as the starch liquefying enzyme.
A -amylase
____________ hydrolyzes a -1,4 glycosidic bonds on the nonreducing ends of amylose and produces maltose residues. B-amylase is known as a saccharifying enzyme.
B-amylase
________ in the amylopectin fraction of starch are hydrolyzed by glucoamylase, which is also known as a saccharifying enzyme.
1.6 glycosidic linkages
In the United States on the average, nearly _________ is produced by the enzymatic hydrolysis of starch.
1.3 × 109 𝑙𝑏/𝑦𝑟 of glucose
The ___________ also hydrolyzes 1,6 glycosidic linkages in starch selectively.
enzyme pullulanase
___________ are used in the hydrolysis of cellulose and are produced by some Trichoderma species, such as Trichoderma viride or T. reesei; and by some molds such as Aspergillus Niger and Thermomonospora, and by some Clostridium species.
Cellulases
________ is an enzyme complex and its formation is induced by cellulose. Trichoderma cellulase hydrolyzes crystalline cellulose, but A. cellulase does not.
Cellulase
_________ is first hydrolyzed to cellobiose by cellulase, and cellobiose is further hydrolyzed to glucose by b-glucosidase. Both of these enzymes are inhibited by their end products, cellobiose and glucose.
Cellulose
__________ are used in cereal processing, alcohol fermentation from biomass, brewing, and waste treatment.
Cellulases
____________ hydrolyze hemicellulose to five-carbon sugar units and are produced by some molds, such as white rot fungi and A. niger.
Hemicellulases
__________________ are used in combination with other enzymes in baking doughs, brewing mashes, alcohol fermentation from biomass, and waste treatment.
Hemicellulases
___________ are used to hydrolyze lactose in when to glucose and galactose and are produced by yeast and some A. species.
Lactases
____________ are used in the fermentation of cheese.
Lactases
Other _____________ produced by Bacillus amyloliquefaciens, A. niger, and Penicillium emersonii are used in brewing mashes containing barley or malt. These enzymes improve wort filtration and extract yield.
microbial glucanases
___________ is used by the antibiotic industry to convert penicillin G to 6- aminopenicillanic acid (6-APA), which is a precursor for semisynthetic penicillin derivatives.
Penicillin acylase
For the ____________ to L-aspartate by aspartase, in industry, this conversion is realized in a packed column of immobilized dead E. coli cells with active aspartase enzyme.
conversion of fumarate
____________ solution is passed through the column, and aspartate is obtained in the effluent stream.
Fumarate
___________ is further coupled with Lphenylalanine to produce aspartame, which is a low-calorie sweetener known as “NutraSweet”.
Aspartate
The conversion of ___________ by immobilized glucose isomerase is an important industrial process.
glucose to fructose
___________ is nearly 1.7 times sweeter than glucose and is used as a sweetener in softdrinks.
Fructose
__________ are commonly used in medicine for diagnosis, therapy, and treatment purposes.
Enzymes
____________ can be used as an anti-inflammatory agent.
Trypsin
______________ is used as an anti-inflammatory agent.
Streptokinase
____________ is used in dissolving and preventing blood clots.
Urokinase
______________, which catalyzes the conversion of L-asparagine to L-aspartate, is used as an anticancer agent.
Asparaginase
Cancer cells require_____________ and are inhibited by asparaginase.
L-asparagine
_________________ is produced by E. coli.
Asparaginase
____________catalyzes the oxidation of glucose to gluconic acid and hydrogen peroxide, which can be easily detected. Glucose oxidase is used for the determination of glucose levels in blood and urine.
Glucose Oxidase
____________ hydrolyze penicillin and are used to treat allergic reactions against penicillin.
Penicillinases
___________________ and ________________ are used in the dissolution of blood clots (particularly following a heart attack or stroke).
Tissue plasminogen activator (TPA) and streptokinase
The development of _____________ as integral component is proceeding rapidly. Two examples of immobilized enzyme electrodes are those used in the determination of glucose and urea by using glucose oxidase and urease immobilized on the electrode membrane, respectively
biosensors using enzymes
___________________ are produced by yeast and Aspergillus.
lactases
