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Topic: Rate of enzyme mediated reactions

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	Enzyme kinetics - Wikipedia, the free encyclopedia
		Enzyme kinetics is the study of the rates of chemical reactions that are catalysed by enzymes.
		Enzyme assays are laboratory procedures that measure the rate of enzyme reactions.
		Enzyme intermediates contain substrates A and B or products P and Q. As shown on the right, enzymes with a ping-pong mechanism can exist in two states, E and a chemically modified form of the enzyme E; this modified enzyme* is known as an intermediate.
	en.wikipedia.org /wiki/Enzyme_kinetics (4263 words)

	Enzymes
		Enzymes are also usually highly selective in terms of their substrates, be it another protein or other compound such as lipids, sugars, or nucleic acids.
		Enzymes increase the rate of biological reactions without altering reaction equilibria: all chemical reactions can be described on the basis of equilibrium; that is, the degree to which a reaction will proceed forward to yield a product or backwards to the starting point.
		The same holds true for enzymes and there are often key amino acids that participate in catalysis that reside at quite a distance from one another in the linear sequence but are spatially close together in the 3-D version of the enzyme.
	neurobio.drexel.edu /GalloWeb/loudon_enzymes.htm (2945 words)

	More on Enzyme
		Enzymes are necessary within biological cells to control molecular shapes and because many chemical reactions would occur too slowly to sustain life; oxidation of organic food compounds to provide energy, for instance.
		Enzymes can couple two or more reactions, so that a thermodynamically favourable reaction can be used to "drive" a thermodynamically unfavorable one, in effect running the reaction 'backwards', or 'uphill'.
		Enzymes are essential to living organisms, and a malfunction of even a single enzyme out of approximately 2,000 types present in our bodies can lead to severe or lethal illness.
	www.psyhist.com /enzyme.htm (3099 words)

	Kidney Enzyme -- Recommendations and Resources (Site not responding. Last check: 2007-11-03)
		Like any catalyst, enzymes work by lowering the activation energy of a reaction, thus allowing the reaction to proceed to its steady state or completion much faster than it otherwise would; the enzyme (again, as with any catalyst) remains unaltered by the completed reaction and can therefore continue catalysis.
		An enzyme can, however, run a normally non-spontaneous reaction 'backwards' by coupling it to a spontaneous one, as long as the net free energy from the total of both reactions is negative.
		Enzymes are necessary within biological cells because most chemical reactions required by the cell would occur too slowly to sustain life; oxidation of organic food compounds to provide energy is one example.
	www.becomingapediatrician.com /health/83/kidney-enzyme.html (1189 words)

	Catalase Project (Site not responding. Last check: 2007-11-03)
		Enzymes are biological catalysts that carry out the thousands of chemical reactions that occur in living cells.
		The enzyme and substrate are held together in an enzyme-substrate complex by hydrophobic bonds, hydrogen bonds and ionic bonds.
		This catalase-mediated reaction is extremely important in the cell because it prevents the accumulation of hydrogen peroxide, a strong oxidizing agent which tends to disrupt the delicate balance of cell chemistry.
	www.hamline.edu /depts/biology/courses/biocon2/Catalase.html (1797 words)

	Enzymes
		For the reaction to occur, you must have both the substrate (catechol) and an enzyme source (potato extract) in the same tube.
		Enzymes, as are all proteins, are sensitive to pH.
		The reaction that required CO to proceed was at maximum speed.
	www.utdallas.edu /~msweet/bioenz.htm (707 words)

	Governor’s School Biology
		Enzymes are globular proteins, responsible for most of the chemical activities of living organisms.
		Enzymes are extremely efficient and may be used over and over again.
		rate of reaction is the slope of the linear portion to the curve.
	rvgs.k12.va.us /faculty/cbohland/gsb/labs/enzyme_catalysis.htm (1069 words)

	Chemical kinetics - Wikipedia, the free encyclopedia (via CobWeb/3.1 planetlab2.cs.unc.edu) (Site not responding. Last check: 2007-11-03)
		The main factors that influence the reaction rate include: the physical state of the reactants, the concentrations of the reactants, the temperature at which the reaction occurs, and whether or not any catalysts are present in the reaction.
		In a reversible reaction, chemical equilibrium is reached when the reaction rate of the forward reaction is equal to the rate of the reverse reaction and the concentrations of the reactants and products no longer change.
		The kinetic isotope effect is a difference in the rate of a chemical reaction when an atom in one of the reactants is replaced by one of its isotopes.
	en.wikipedia.org.cob-web.org:8888 /wiki/Chemical_kinetics (1159 words)

	Enzymes & Celiac
		Although the protein can antagonize the situation (and cause the peptide probelm), the enzymes needed to break down the part of gliadin reactive to celiacs are the amylases and some subgroups of amylases (other enzymes that work on starch bonds such as glucoamylases).
		Because the fragment is rich in the amino acid proline, investigators reasoned that a peptidase (an enzyme that breaks down proteins) with the ability to digest proline-rich chains might be able to break down the gliadin fragment, rendering it harmless to celiac patients.
		In addition, the enzyme operates best in just the kind of physiological environment found in the human stomach and works 60 times faster than an earlier promising enzyme, which was not effective in acidic conditions and was inactivated by pepsin, both of which are found in the stomach.
	www.enzymestuff.com /conditionceliac.htm (5564 words)

	An Enzyme- Substrate Model
		To study reaction rates of an enzyme-mediated reaction.
		Making the reaction more concrete by using objects that can be readily seen and handled offers a possible solution.
		Enzymes, like all proteins, tend to change shape at high temperatures, when in contact with strong acids or bases, or when exposed to heavy metal ions.
	www.accessexcellence.org /AE/AEPC/WWC/1991/enzyme_substrate.html (819 words)

	Abasic Sites Stimulate Double-stranded DNA Cleavage Mediated by Topoisomerase II -- Kingma et al. 270 (37): 21441 -- ...
		Rather than acting by inhibiting the catalytic activity of the enzyme, anticancer drugs dramatically increase levels of covalent topoisomerase II-cleaved DNA complexes that are normal, but fleeting intermediates in the catalytic cycle of the enzyme(1, 2, 3, 4).
		Reactions were stopped by the addition of 1 M Tris-HCl, pH 7.9, at 4 °C followed by buffer exchange into 10 mM Tris-HCl, pH 7.9, 0.1 mM EDTA in a Bio-Spin 6 chromatography column (Bio-Rad).
		It is notable, however, that catalytic DNA relaxation is limited by the rate at which the enzyme releases its fully relaxed DNA substrate(39).
	www.jbc.org /cgi/content/full/270/37/21441 (3882 words)

	Preparing for the MCAT
		The rate of any reaction is determined by the energy it takes to achieve the transition state.
		Enzymes are specific for particular reactions using particular substrates.
		The first enzyme in the pathway, then, threonine dehydratase, is regulated by the presence or absence of isoleucine.
	nas.cl.uh.edu /novotny/mcatb1.htm (1417 words)

	REACTIONS & ENZYMES
		Reactions that require energy to initiate the reaction are known as endergonic reactions.
		Enzymes can act rapidly, as in the case of carbonic anhydrase (enzymes typically end in the -ase suffix), which causes the chemicals to react 107 times faster than without the enzyme present.
		The functioning of the enzyme is determined by the shape of the protein.
	www.emc.maricopa.edu /faculty/farabee/BIOBK/BioBookEnzym.html (1582 words)

	Enzymes-- Biotechnology Stocks
		activation energy of a reaction, thus allowing the reaction to proceed to its steady state or completion much faster than it otherwise would; the enzyme (again, as with any catalyst) remains unaltered by the completed reaction and can therefore continue catalysis.
		run a normally nonspontaneous reaction 'backwards' by coupling it to a spontaneous one, as long as the net free energy from the total of both reactions is negative.
		inhibited somehow; in a similar vein, purifications of other enzymes that begin with a preparation containing a protease will often result in loss of the enzyme being purified unless the protease is inhibited or inactivated.
	www.edinformatics.com /biotechnology/enzymes.htm (2413 words)

	Arctic and Alpine Research: (Site not responding. Last check: 2007-11-03)
		The study communities included lichen-heath, a sparse community vegetated by lichens and dwarf ericaceous shrubs on rocky soils, moist Cassiope dwarf-shrub heath tundra, dominated by Carex and evergreen and deciduous shrubs on relatively deep organic soils, and dry Cassiope dwarf-shrub heath of stone-stripe areas, which was of intermediate character.
		Rates of CO efflux were similar for the three communities until mid-season when they peaked at rates between 4.9 and 5.9 g m
		Rates of carbon dioxide efflux followed changes in soil temperature early in the season when soil moisture was highest.
	instaar.colorado.edu /AAAR/volume28/28-3abs.html (3380 words)

	Preventable Adverse Drug Reactions: A focus on drug interactions
		Since Phase II reactions generally result in conjugation of a drug to a water-soluble group like a sugar, peptide (glutathione) or sulfur group, and, because there is a large excess of these groups in well nourished cells, these reactions are rarely rate-limiting.
		As shown in the slide, the enzymes function in a cascade of oxidation-reduction reactions that ultimately result in one atom of oxygen being incorporated into an oxidized metabolite, such as the hydroxylated form of drug shown in the slide.
		The enzymes are named according to families that are defined by the similarity of their amino acid sequence.
	www.fda.gov /cder/drug/drugReactions (8655 words)

	eMedicine - Biotin Deficiency : Article by Noah S Scheinfeld, MD, JD, FAAD (Site not responding. Last check: 2007-11-03)
		In the first reaction, the biotin moiety of a carboxylase is carboxylated at the nitrogen atom diagonally across from the valeric acid substituent (see Image 2).
		In the second reaction, the CO moiety is transferred to the substrate (causing it to be carboxylated in the process), and the original carboxylase is liberated intact, ready to perform another carboxylation.
		In the lysosomes, various proteolytic enzymes degrade the holocarboxylase to form biocytin, which in turn, is hydrolyzed by biotinidase to form biotin and lysine.
	www.emedicine.com /ped/topic238.htm (4430 words)

	an enzyme lab
		If you leave them in there for a much longer period and the color still says the same, you can make a reasonable assumption that the reaction is complete and the shade of red you see is as intense as it is going to get.
		Another thought: Increasing the amount of enzyme or bile (or both) in another sample might also possibly yield different results if we had been working with weak concentrations of these substances.
		Since the enzymes are released unchanged, after mediating a reaction, they will go work on other fat particles until all are broken down.
	www.physicsforums.com /showthread.php?p=942747 (1716 words)

	Mechanisms of enzyme (Site not responding. Last check: 2007-11-03)
		(B2) A reactant that is close in shape to the active site may compete with the normal substrate and decrease the rate of the reaction.
		(C) An excess of substrate slows the rate of reaction.
		(D) An increase in the enzyme concentration will increase the rate of reaction since the substrate does not have to wait for a free active site.
	cas.bellarmine.edu /tietjen/mechanisms_of_enzyme.htm (111 words)

	Enzyme Biochemistry Practice Problems (Site not responding. Last check: 2007-11-03)
		You are a research scientist studying a novel enzyme X, and you want to characterize this new enzyme.
		Five reaction mixtures containing 10 x 10-9 M of an enzyme are made up with five different substrate concentrations and the initial rates of the reactions were measured:
		You measure the initial velocity of the reaction (rate at which lactose is cleaved) at varying concentrations of substrate.
	web.mit.edu /esgbio/www/eb/problems.html (1248 words)

	Comparison of Metal-Ion-Dependent Cleavages of RNA by a DNA Enzyme and a Hammerhead Ribozyme
		The cleavage activity of the DNA enzyme was pH dependent, and the logarithm of the cleavage rate increased linearly with pH from pH 6 to pH 9 with a slope of approximately unity.
		Addition of La ions to the Mg -background reaction mixture inhibited the DNA enzyme-catalyzed reactions, suggesting the replacement of catalytically and/or structurally important Mg ions by La ions.
		Similar kinetic features of DNA enzyme mediated cleavage of RNA and of hammerhead ribozyme-mediated cleavage suggest that a very similar catalytic mechanism is used by the two types of enzyme, despite their different compositions.
	pubs.acs.org /cgi-bin/abstract.cgi/bomaf6/2002/3/i01/abs/bm010095c.html (290 words)

	activator \| \| Dictionary & Translation by Babylon
		Activator (proteomics), a type of effector that increases the rate of enzyme mediated reactions
		Activator (genetics), a DNA-binding protein that regulates one or more genes by increasing the rate of transcription
		n : any agency bringing about activation; (biology) a molecule that increases the activity of an enzyme or a protein that increases the production of a gene product in dna transcription [ant: inhibitor]
	www.babylon.com /definition/activator/All (234 words)

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