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Topic: Tetrahedral intermediate

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	Serine protease - Wikipedia, the free encyclopedia
		As the polypeptide enters, the above described process occurs: the serine -OH attacks the carbonyl carbon, the nitrogen of the histidine accepts the hydrogen from the -OH of the [serine] and a pair of electrons from the double bond of the carbonyl oxygen moves to the oxygen.
		When the tetrahedral intermediate of step 1 and step 3 are generated, the negative oxygen ion, having accepted the electrons from the carbonyl double bond fits perfectly into the oxyanion hole.
		There are certain inhibitors which resemble the tetrahedral intermediate, and thus fill up the specificity pocket, preventing the enzyme from working properly.
	en.wikipedia.org /wiki/Serine_protease (1552 words)

	Presentation3 (Site not responding. Last check: 2007-11-04)
		Nucleophilic attack by water on the acyl intermediate on ser195 and abstraction of a proton from water by His 57 leads to the formation of a second tetrahedral intermediate.
		Collapse of tetrahedral intermediate leading to the cleavage of C-O acyl bond to ser195, reprotonation of Ser195 by His 57 and regeneration of catalytic triad.
		Oxyanion of the reaction intermediate is presumed to be stabilized by the oxyanion hole made by the amide nitrogens of Gly193, Asp 194 and Ser 195.
	www.arches.uga.edu /~kumarj/bcmb8010/pres3.html (129 words)

	Untitled Document (Site not responding. Last check: 2007-11-04)
		The segments were covalently joined by a phosphoramidate linkage with tetrahedral geometry, which geometry is proposed to mimic the tetrahedral intermediate of the transition state.
		This is not the case for the tetrahedral intermediate, where the transition state is chiral and is likely to be specific to one diastereomer.
		The phosphoramidate mimics the tetrahedral geometry of the transition state during peptide bond formation.
	www.mbb.yale.edu /up/up_02_ex.htm (1420 words)

	243april9.html
		The resulting protonated tetrahedral intermediate is in equilibrium with the nonprotonated form.
		The H+ increases the rate of formation of the tetrahedral intermediate, because the protonation of the carbonyl carbon increases the susceptibility of a nucleophilic attack.
		The H+ increases the rate of collapse of the tetrahedral intermediate by decreasing the basicity of the leaving group.
	spot.pcc.edu /~chandy/243/243april9.html (495 words)

	Introduction
		During the second step or deacylation, the acyl-enzyme intermediate is hydrolyzed by a water molecule to release the peptide and to restore the Ser-hydroxyl of the enzyme.
		The catalytic mechanism leads to the formation of a non covalent tetrahedral intermediate after the attack of a zinc-bound water molecule on the carbonyl group of the scissile bond.
		This intermediate is further decomposed by transfer of the glutamic acid proton to the leaving group.
	delphi.phys.univ-tours.fr /Prolysis/introprotease.html (1184 words)

	[No title] (Site not responding. Last check: 2007-11-04)
		This is the first of two intermediates of this type to form in the proposed mechanism of catalysis by serine proteases.
		This is an important part of the mechanism because the data collected with the simple amide and ester substrates showed that a partially stable (metastable) covalent intermediate formed between the substrate and the enzyme.
		This tetrahedral intermediate decomposes then with bond rearrangements and leads to the formation of the second product and returns the enzyme to its starting state so that it can catalyze another round of the reaction of water with the protein or peptide where the amide bond is hydrolyzed.
	www.bio.mtu.edu /campbell/401lec15Bp6.html (481 words)

	Serine protease - Open Encyclopedia (Site not responding. Last check: 2007-11-04)
		The catalysis of the peptide cleavage can be seen as a ping-pong catalysis, in which a substrate binds (in this case, the polypeptide being cleaved), a product is released (the n-terminus 'half' of the peptide), another substrate binds (in this case, water), and another product is released (the c-terminus 'half' of the peptide).
		As the polypeptide enters, the above described process occurs: the serine -OH attacks the carbonyl carbon, the nitrogen of the hystidine accepts the hydrogen from the -OH of the [serine] and a pair of electrons from the double bond of the carbonyl oxygen moves to the oxygen.
		The covalent electrons creating this bond move to attack the hydrogen of the hystidine, breaking the connection.
	www.open-encyclopedia.com /Serine_protease (1357 words)

	[No title] (Site not responding. Last check: 2007-11-04)
		In this concept, an intermediate form exists between the substrates and products in an enzyme catalyzed reaction and this intermediate is called the transition-state intermediate, just as it is in chemistry.
		On the way to forming products P + Q, the reaction goes through an intermediate which is neither the substrates nor the products and is 'intermediate' between them - so it is called an intermediate and since it is going through the transition from substrates to products it is called the transition-state intermediate.
		The transition-state intermediate in the trypsin catalyzed hydrolysis of a peptide bond.
	www.bio.mtu.edu /campbell/401l18p2.html (487 words)

	Searle Scholar Profile : Gregory K. Farber (1991)
		In some cases, different intermediates which precede a rate determining step can be trapped by flowing substrate through a crystal (a steady state experiment) rather than by allowing the system to come to equilibrium.
		The first project that we have attempted is to trap the tetrahedral intermediate of reaction catalyzed by chymotrypsin.
		We have been able to trap the tetrahedral intermediate (in the peptide bond synthesis direction) in the crystal in hexane.
	www.searlescholars.net /people/1991/farber.html (645 words)

	Myron Lee Bender, May 20, 1924—July 29, 1988 \| By Frank H. Westheimer \| Biographical Memoirs
		He arrived with an original research plan--a method to test for the reality of the tetrahedral intermediate that had long been postulated in the hydrolysis of the esters and amides of carboxylic acids.
		The data, both from Bender's laboratory and from that of his critics, show that the exchange of isotopic oxygen in many cases accompanies the alkaline hydrolysis of esters and it is reasonable that, in some instances, the ratios of rate constants in the scheme above are such as to obscure that exchange.
		These data are consistent with rapid reaction of esters with the enzyme, followed by rate-limiting hydrolysis of a common intermediate, whereas the amide is hydrolyzed with rate-limiting acylation of the enzyme.
	www.nap.edu /readingroom/books/biomems/mbender.html (3310 words)

	Adenosine deaminase converts purine riboside into an analogue of a reactive intermediate: a 13C NMR and kinetic study.
		Adenosine deaminase converts purine riboside into an analogue of a reactive intermediate: a 13C NMR and kinetic study.The 13C NMR spectra of [2-13C]- and [6-13C]purine ribosides have been obtained free in solution and bound to the active site of adenosine deaminase.
		The positions of the resonances of the bound ligand are shifted relative to those of the free ligand as follows: C-2, -3.7 ppm; C-6, -73.1 ppm.
		Enzymic stabilization of this intermediate may be an important catalytic strategy used by the enzyme to lower the standard free energy of the preceding transition state.
	www.pdg.cnb.uam.es /UniPub/iHOP/gp/5723735.html (293 words)

	Nat' Academies Press, (NAS Colloquium) Proteolytic Processing and Physiological Regulation (1999) (Site not responding. Last check: 2007-11-04)
		Colloqium on Proteolytic Processing and Physiological Regulation attacking nucleophile and stabilization of a tetrahedral intermediate-transition state in 3C proteases closely resembles that of trypsin-like serine proteases, suggesting that the viral 3C proteases are related mechanistically to serine proteases rather than to the papain-like cysteine proteases.
		The affinity of peptide aldehyde inhibitors for trypsin-like serine proteases has been attributed to their ability to form, with the active-site serine, hemiacetals that resemble the transition state in amide hydrolysis, with the oxyanion stabilized in a structurally conserved oxyanion hole.
		In the absence of bound ligands, the corresponding residues in rhinovirus, poliovirus, and hepatitis A 3C proteases exist in multiple conformations and/or are highly mobile, as evidenced by average temperature factors of 50–60 Å2.
	www.nap.edu /books/030906645X/html/11000.html (7497 words)

	reactivityacidderivatives
		Recall that in the case of aldehydes and ketones, the tetrahedral intermediate picked-up a proton to complete the reaction.
		This explains why the tetrahedral intermediate obtained by the addition of a nucleophile will not "attempt" to regenerate the carbonyl group (by having to force hydride ion out).
		On the other hand, the tetrahedral intermediate obtained by the addition of a nucleophile to an acid chloride will be more than delighted to reform the C=O by loosing chloride ion.
	www.wiu.edu /users/mftkv/Chem332/reactivityacidderivatives.html (327 words)

	[No title]
		The carbonyl carbon rehybridizes from sp2 to sp3, and the intermediate that is formed has a tetrahedral geometry.
		The cyanide ion reacts as a typical nucleophile with the electrophilic carbonyl carbon to form a tetrahedral intermediate.
		The alkoxide ion tetrahedral intermediate abstracts a proton from water to generate the neutral gem diol product and to regenerate the hydroxide ion catalyst.
	www.chem.wisc.edu /~newtrad/CurrRef/AIDStopic/AIDS.AldKetRxns.html (2217 words)

	BC Online: 7B - Mechanisms of Enzyme Catalysis
		The tetrahedral intermediate then collapses, expelling the leaving amine group, which picks up a proton from Glu 270, which now acts as a general acid catalyst.
		These include nucleophilic catalysis (with the Ser 195 forming a covalent intermediate with the substrates), general acid/base catalysis with His 57, and loosely, electrostatic catalysis with Asp 102 stabilizing not the transition state or intermediate, but the protonated form of Hs 57.
		This oxyanion hole is occupied in the tetrahedral intermediate.
	employees.csbsju.edu /hjakubowski/classes/ch331/catalysis/olcatenzmech.html (4749 words)

	Graphics Gallery: Lipids & Membranes
		The product of the rate-determining step is a tetrahedral intermediate resulting from addition of hydroxide ion to the the ester carbonyl.
		Because this intermediate is near the transition state on the progress-of-reaction curve for this process, the transition state must therefore be structurally very similar to this tetrahedral intermediate.
		Compare the phosphodiester group at C2 of the glycerol to the tetrahedral intermediate in ester hydrolysis -- they are very similar in geometry and electronic structure.
	www.usm.maine.edu /~rhodes/BiochemViews/LipMemb (2135 words)

	Centre of Excellence in Biocrystallography - ITALY
		The second step was the "in-site" substrate construction on the basis of GRID molecular field interactions, and the simulation of tetrahedral intermediates.
		The combined use of GRID and tetrahedral intermediate construction has also provided explanation of the observed enantioselectivity of PGA towards L-enantiomers of aromatic aminoacids.
		The docking simulation and the conformational search of the tetrahedral intermediates show that L- aminoacids and their esters position their carbonyl group in the polar zone mentioned before, taking good interactions with a number of polar residues, in particular the Arg B:263, while their side chains find a room in the hydrophobic zone.
	www.univ.trieste.it /~ceb/gardossi.html (853 words)

	Post Doctoral Research Summary
		This reaction results in the formation of the charged tetrahedral intermediate that spontaneously resolves into the newly formed peptide bond and the release of the tRNA hydroxyl leaving group.
		After nucleophilic attack, the charged tetrahedral intermediate and/or leaving group hydroxyl could be stabilized by the 2'-OH of the P-site CCA fragment or other RNA moieties within the active site (Muth et al, in preparation).
		The chiral phosphorous structure serves as a stable functionality that represents the correct charge and geometry of the tetrahedral intermediate formed during the peptidyl transfer reaction.
	www.stolaf.edu /people/muth/PostDocProject.html (681 words)

	460
		Thus a nucleophilic oxygen of activated water attacks the carbonyl carbon to form a negatively charged tetrahedral intermediate.
		The chymotrypsin-substrate intermediate is covalently bound to the enzyme.
		The reaction goes through a tetrahedral intermediate which is relatively unstable and converts readily to the acyl intermediate which is quite stable.
	www.biochem.arizona.edu /classes/bioc460/spring/html/LEC12.html (332 words)

	Myron Lee Bender, May 20, 1924—July 29, 1988 \| By Frank H. Westheimer \| Biographical Memoirs
		This is what would be predicted if the formation of the tetrahedral intermediate is reversible and if the intermediate is sufficiently long-lived to undergo proton transfer before decomposition.
		One must accept the tetrahedral intermediate by analogy, rather than demonstrate it by experiment.
		These equations can be simplified when either the first step (acylation of the enzyme to form an acylated enzyme as intermediate) or the second step (hydrolysis of this intermediate) is clearly rate-limiting.
	stills.nap.edu /html/biomems/mbender.html (3310 words)

	Structural studies of arginase isozymes.
		The tetrahedral sulfonamide group displaces the metal-bridging hydroxide ion pf the native enzyme and bridges the binuclear manganese cluster with an ionized NH- group.
		The binding mode of the sulfonamide inhibitor may mimic the binding of the tetrahedral intermediate and its flanking transition states in catalysis.
		The three-dimensional structures of D128E, D128N, D232A, D232C, D234E, H101N and H101E arginases I have been determined by X-ray crystallographic methods to elucidate the roles of the first-shell metal ligands in the stability and catalytic activity of the enzyme.
	repository.upenn.edu /dissertations/AAI3109159 (356 words)

	ICE
		The tetrahedral bond geometry explains the openness and relatively low density of the ice Ih structure.
		In the higher-pressure phases the tetrahedral bonding geometry is distorted; the bond angles are bent from perfect tetrahedral and the H-bonds are stretched.
		There are six different orientations possible for a water molecule in its tetrahedral bonding environment, each corresponding to a different arrangement of protons in its four H-bonds.
	skua.gps.caltech.edu /hermann/ice.htm (1983 words)

	Serine Proteases (Site not responding. Last check: 2007-11-04)
		Whether a tetrahedral intermediate is formed was a point of considerable contention in the early investigations of protease mechanisms; biochemists tended to draw nucleophilic acyl substitutions as if they were S
		In short, a tetrahedral intermediate MUST form because the orbital construction of the substrate won't permit any other pathway.
		Here's the tetrahedral intermediate, bound to Ser195 with the former carbonyl oxygen in the "oxyanion hole".
	chemistry.umeche.maine.edu /CHY252/Peptidase3.html (807 words)

	Geometry and Energy of Amidoenethiolate Conformers formed (Site not responding. Last check: 2007-11-04)
		In an attempt to address this question, a series of ring-opened enethiolate systems and their corresponding tetrahedral intermediates have been subjected to theoretical study: first, in order to obtain the geometries and relative energies of the enethiolate rotamers and second, in order to locate the tetrahedral intermediate into which they transform.
		Optimized structures and charges for the tetrahedral intermediates of series a are shown in Figures 5a and 5b, respectively.
		As in the less substituted tetrahedral intermediates, these were found to be minima on the potential surface: i.e., no imaginary frequencies were found.
	www.arkat-usa.org /ark/journal/2001/I12_Tee/313/313.asp (2582 words)

	Media Portfolio (Site not responding. Last check: 2007-11-04)
		This geometry is represented by sp3 hybridization of nitrogen, with the bulky lone pair compressing the H-N-H bond angles to 107o from the "ideal" sp3 bond angle of 109.5o.
		The nitrogen of the amine attacks the carbonyl carbon forming a tetrahedral intermediate.
		The nitrosonium ion appears to be the reactive intermediate in most reactions of amines with nitrous acid.
	wps.prenhall.com /wps/media/objects/340/348272/wade_ch19.html (2689 words)

	The gem-dimethyl effect in reactions through tetrahedral intermediates (Site not responding. Last check: 2007-11-04)
		The role of steric repulsions in the tetrahedral intermediate was excluded because the acid-catalyzed cyclization showed a normal GDME.
		The latter hindrance arises in the ring intermediate because the oxygen atom of the ethoxy group is flanked by the gem-dimethyl group on one side and the substituent R
		And secondly, the intermediate should not be in equilibrium with the reagents at least in one of the modes.
	www.arkat-usa.org /ark/journal/2001/I12_Tee/311/311.asp (3828 words)

	[No title] (Site not responding. Last check: 2007-11-04)
		The mechanisms of all nucleophilic addition reactions share a common step: addition of a nucleophile to a carbonyl carbon to form a tetrahedral intermediate.
		The final product of nucleophilic addition reactions depends on what happens to the tetrahedral intermediate that is formed.
		Protonation of the intermediate to generate an alcohol is common, however elimination reactions to form unsaturated products can also occur.
	www.odu.edu /sci/jadamski/notes/19h.htm (114 words)

	T to Z
		The steps in a chain reaction in which reactive intermediates are destroyed or rendered inactive, thus ending the chain.
		A reaction intermediate in which the bond arrangement around an initially double-bonded carbon atom (typically a carbonyl carbon atom) has been transformed from trigonal to tetrahedral.
		The interception of a reactive molecule or reaction intermediate so that it is removed from the system or converted into a more stable form for study or identification.
	www.chem.qmw.ac.uk /iupac/gtpoc/TtZ.html (1773 words)

	Abstract
		One, it allows the type II reverse turn to occur that places catalytic Ser195 in the proper spatial orientation with the other two residues, His57 and Asp102, of the catalytic triad.
		Two, the backbone NH-group of Gly193 participates in stabilization of the transition state tetrahedral intermediate by forming a H-bond with the negatively charged oxygen of the substrate in the oxyanion hole.
		Moreover, the active conformation of the enzyme is stabilized by a H-bond between the carboxylate of Asp194 and the NH -terminus of residue 16.
	www.blackwellpublishing.com /isth2003/abstract.asp?id=8151 (384 words)

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