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PubMed2006

Di-, tri-, and tetranuclear zinc hydroxamate complexes as structural models for the inhibition of zinc hydrolases by hydroxamic acids.

Attempts to produce Zn analogues of the structural model complexes [M2(mu-O2CR)2(O2CR)2(mu-H2O)(tmen)2] (M = Ni, Co, Mn; R = CH(3), C(CH3)3, CF3) by the reaction of a series of zinc carboxylates with N,N,N',N'-tetramethylethylenediamine (tmen), resulted in the mononuclear complexes [Zn(OAc)(2)(tmen)] (1) and [Zn(crot)2(tmen)].(0.5)H2O (2) for R = CH3 and (CH)2CH3, respectively, and the dinuclear complexes [Zn(2)(mu-piv)(2)(piv)(2)(mu-H2O)(tmen)2] (3) and [Zn2(mu-OAc(F))2(OAc(F))2(mu-H2O)(tmen)2] (4) for R = C(CH3)3 and CF3, respectively. In contrast to the analogous imidazole series, i.e., [M2(mu-O2CR)2(O2CR)2(mu-H2O)(Im)4] (M = Ni, Co, Mn; R = CH3, C(CH3)3, CF3), zinc carboxylates react with imidazole to give only the mononuclear complexes [Zn(OAc)2(Im)2] (5), [Zn(crot)2(Im)2].H2O (6), [Zn(piv)2(Im)2].(0.5)H2O (7), and [Zn(OAc(F))2(Im)2] (8). Reaction of 1, 2, and 3 with either acetohydroxamic acid (AHA) or benzohydroxamic acid (BHA) gives the dinuclear complexes [Zn2(O2CR)3(R'A)(tmen)], where R'A = acetohydroxamate (AA) (9, 10, 11) or benzohydroxamate (BA) (13, 14, 15). In these complexes, the zinc atoms are bridged by a single hydroxamate and two carboxylates, with a capping tmen ligand on one zinc and a monodentate carboxylate bonded to the second zinc atom. This composition models closely the observed structure of the active site of the p-iodo-d-phenylalanine hydroxamic acid inhibited Aeromonas proteolyticaaminopeptidase enzyme. In contrast, 4 reacts with AHA to give [Zn2(OAc(F))3(tmen)2(AA)] (12) with an additional tmen ligand so that both Zn atoms are 6-coordinate, whereas reaction with BHA gives the trinuclear complex [Zn3(OAc(F))4(tmen)2(BA)2] (16). Reactions of 3 and 4 with glutarodihydroxamic acid (GluH2A2) produce the tetranuclear complexes [Zn4(piv)6(tmen)4(GluA2)] (18) and [Zn4(OAc(F))6(tmen)4(GluA2)] (19).

Aeromonas↗
PubMed1985

Crystallization of cytoplasmic actin in complex with deoxyribonuclease I.

Crystals of cytoplasmic (porcine liver) actin in complex with deoxyribonuclease I (DNAase I) were prepared for structural determination by X-ray-diffraction analysis. The crystallization of porcine liver actin-DNAase I complex is preceded by a brief treatment with immobilized trypsin, whereby a C-terminal tri- or di-peptide including cysteine-374 is removed from the actin without any noticeable degradation of both proteins as judged by sodium dodecyl-sulphate/polyacrylamide-gel electrophoresis. Analysis of the crystals obtained does not reveal any differences in the three-dimensional structure of porcine liver actin from its skeletal compartment at up to 0.6 nm resolution. However, in contrast with crystalline skeletal-muscle actin-DNAase I complex, heavy-atom substitution of crystals of porcine liver actin-DNAase I complex could not be achieved with methyl mercuriacetate. Evidence is presented that, in porcine liver actin, the N-terminal cysteine residue is not located at position no. 10, as in skeletal- and smooth-muscle actin, but most probably at position no. 17. Thus, because this site is covered by DNAase I, the cysteine becomes inaccessible to titration with 5,5'-dithiobis-(2-nitrobenzoic acid) after complex-formation with DNAase I.

Actins↗
PubMed2006

Effective acceleration of atom transfer carbonylation of alkyl iodides by metal complexes. Application to the synthesis of the hinokinin precursor and dihydrocapsaicin.

[reaction: see text] Atom transfer carbonylation (ATC) of alkyl iodides leading to carboxylic acid esters is effectively accelerated by Pd(PPh(3))(4) and Mn(2)(CO)(10) under photoirradiation conditions. In the presence of amines, Pd(0) complexes affected double carbonylations leading to alpha-keto amides, whereas Mn(2)(CO)(10) accelerated only a single carbonylation reaction leading to the corresponding amides. The Pd(0)-accelerated ATC system was successfully applied to the synthesis of hinokinin and dihydrocapsaicin.

4-Butyrolactone↗
PubMed2002

Solvent-metal interactions in bis[1,2-dicarba-closo-dodecaboran(12)-1-yl]mercury(II) dichloromethane solvate and bis[1,12-dicarba-closo-dodecaboran(12)-1-yl]mercury(II) tetrahydrofuran solvate.

The title compounds, bis[1,2-dicarba-closo-dodecaboran(12)-1-yl]mercury(II) dichloromethane solvate, [Hg(C(2)B(10)H(11))(2)].CH(2)Cl(2), (I), and bis[1,12-dicarba-closo-dodecaboran(12)-1-yl]mercury(II) tetrahydrofuran solvate, [Hg(C(2)B(10)H(11))(2)].C(4)H(8)O, (II), were prepared in excellent yields using a robust synthetic procedure involving the reaction of HgCl(2) with the appropriate monolithiocarborane. X-Ray analysis of the products revealed strong interactions between the Hg atoms in both complexes and the respective lattice solvent. The distances between the Hg(II) centers and the Cl atoms of the dichloromethane solvent molecule in the ortho-carborane derivative, (I), and the O atom of the tetrahydrofuran molecule in the para-carborane complex, (II), are shorter than the sums of the van der Waals radii for Hg and Cl (3.53 A), and Hg and O (3.13 A), respectively, indicating moderately strong interactions. There are two crystallographically independent molecules in the asymmetric unit of both compounds, which, in each case, are related by differing relative positions of the cages.

Journal Article↗
PubMed2002

Active-site architecture of endopolygalacturonase I from Stereum purpureum revealed by crystal structures in native and ligand-bound forms at atomic resolution.

Crystal structures of endopolygalacturonase from Stereum purpureum were solved in native and two galacturonic acid complex states at atomic resolution. Endopolygalacturonase catalyzes the hydrolysis of alpha-1,4-glycosidic linkage of polygalacturonate in pectin. The native structure was determined by the multiple wavelength anomalous dispersion method and was refined anisotropically with SHELXL-97, with an R factor of 11.4% and an R(free) factor of 14.0% at 0.96 A resolution. The enzyme folds into a right-handed parallel beta-helix with 10 complete turns. The crystal structures of its binary complex with one D-galacturonate and its ternary complex with two D-galacturonates were also determined to identify the substrate binding site at 1.0 and 1.15 A resolutions, respectively. In the binary complex, one beta-D-galactopyranuronate was found in the +1 subsite, thus proving the strong affinity of the +1 subsite expected from the bond cleavage frequency on oligogalacturonates. In the ternary complex, an additional beta-D-galactofuranuronate was found in the -1 subsite. In both subsites, the recognition of the galacturonate carboxy group is important in galacturonate binding. In the +1 subsite, the carboxy group interacts with three basic residues, His195, Arg226, and Lys228, which were conserved in all endopolygalacturonases. In the -1 subsite, the unique nonprolyl cis-peptide bond is believed to be involved in binding the carboxy group of the substrate. The active site architecture of the complexes provides insight into the mechanism of inverting glycosyl hydrolases and also sheds light on the basis of the differences between the family 28 and the other inverting glycosyl hydrolases.

Amino Acid Sequence↗
PubMed2000

Lipoplex formation under equilibrium conditions reveals a three-step mechanism.

Cellular transfection can be accomplished by the use of synthetic amphiphiles as gene carrier system. To understand the mechanism and hence to improve the efficiency of transfection, insight into the assembly and properties of the amphiphile/gene complex is crucial. Here, we have studied the interaction between a plasmid and cationic amphiphiles, using a monolayer technique, and have examined complex assembly by atomic force microscopy. The data reveal a three-step mechanism for complex formation. In a first step, the plasmids, interacting with the monolayer, display a strong tendency of orientational ordering. Subsequently, individual plasmids enwrap themselves with amphiphile molecules in a multilamellar fashion. The size of the complex formed is determined by the supercoiled size of the plasmid, and calculations reveal that the plasmid can be surrounded by 3 to 5 bilayers of the amphiphile. The eventual size of the transfecting complex is finally governed by fusion events between individually wrapped amphiphile/DNA complexes. In bulk phase, where complex assembly is triggered by mixing amphiphilic vesicles and plasmids, a similar wrapping process is observed. However, in this case, imperfections in this process may give rise to a partial exposure of plasmids, i.e., part of the plasmid is not covered with a layer of amphiphile. We suggest that these exposed sites may act as nucleation sites for massive lipoplex clustering, which in turn may affect transfection efficiency.

Chloramphenicol O-Acetyltransferase↗
PubMed1990

Separation and identification of desferrioxamine and its iron chelating metabolites by high-performance liquid chromatography and fast atom bombardment mass spectrometry: choice of complexing agent and application to biological fluids.

An HPLC-based method capable of separating desferrioxamine (DFO) and its iron chelating metabolites from uv-absorbing species present in biological fluids has been developed. This method relies on the use of nitrilotriacetic acid (NTA) as the complexing agent in the mobile phase, instead of EDTA, previously used in HPLC methods. The use of NTA ensures that iron contamination present in buffers and bound to the column does not interfere with analysis. The disadvantages of using EDTA are discussed. The identity of the iron chelating metabolites of DFO present in the urine of patients with beta-thalassemia major has been established using FAB mass spectrometry. The metabolism of DFO, reported in this study, takes place almost exclusively at the N-terminal region of the molecule and is in many respects similar to the degradation of the amino acid lysine. In addition, a metabolite which corresponds to N-hydroxylation of the terminal amino group has been identified.

Adult↗
PubMed1992

Atomic interactions in protein-carbohydrate complexes. Tryptophan residues in the periplasmic maltodextrin receptor for active transport and chemotaxis.

We have refined the 1.9 A resolution crystal structures of two maltodextrin receptor mutants in which tryptophan residues 230 and 232 have been changed to alanine and compared these structures with the refined 1.7 A structure of the wild-type protein. In the wild-type structure, Trp230, which is located in the maltodextrin-binding groove, stacks against the B-face of the reducing sugar of the bound maltose. Trp232, which is located near the protein surface, does not participate directly in sugar binding. Relative to the wild-type structure, neither mutation caused a significant rearrangement in the overall protein structure or in the mode of binding maltose. Although the position once occupied by Trp230 remains empty, a new water molecule has moved near the void. In contrast, a new water molecule has entered into the space once occupied by Trp232. Whereas one hydrogen bond is formed with the water molecule near the Trp230 void, no hydrogen bond is associated with the water molecule occupying the space vacated by Trp232. The three van der Waals' contacts between Trp230 and maltose in the wild-type structure that are lost in the W230A mutation could contribute to the 12-fold decrease in ligand-binding activity of the mutant protein. The W232A mutation causes little change in binding activity. The structures of these mutant proteins also provide some insight into the complicated tryptophan fluorescence spectra of the maltodextrin binding-protein. The change in fluorescence due to the deletion of Trp230 can readily be explained as resulting directly from loss of Trp230 in the sugar-binding site. The change in fluorescence due to deletion of Trp232, however, is ascribed to the modification of local interactions mediated by the binding of maltodextrin since the tryptophan is not directly involved in any sugar-binding interaction.

Bacterial Proteins↗
PubMed2005

Surface complexation of condensed phosphate to aluminum hydroxide: an ATR-FTIR spectroscopic investigation.

Two model compounds, sodium pyrophosphate (pyro-P) and sodium tripolyphosphate (tripoly-P), were employed to elucidate the binding mechanisms of condensed phosphate on aluminum hydroxide by utilizing attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Peak assignments for the condensed phosphates in the solution phase and those adsorbed on the surface of aluminum hydroxide were made. Electron delocalization and polarization were employed to explain the peak shifts and the complexation of condensed phosphate with aluminum hydroxide. The tripoly-P and pyro-P were adsorbed on aluminum hydroxide by forming inner-sphere complexes. The adsorbed condensed phosphates were deprotonated in the pH range from 4 to 10. Monodentate, bidentate, and binuclear complexes were formed when pyro-P was adsorbed on aluminum hydroxide, while monodentate and binuclear complexes were formed when tripoly-P was adsorbed. Based on the FTIR data, we proposed that when either bidentate or binuclear complexes were formed, the two oxygen atoms participating in the complexation with aluminum hydroxide could not be originated from the same terminal phosphate moiety. The AlO bond formed in the complexation of pyro-P or tripoly-P with aluminum hydroxide (AlPO(-3)) was not as strong as the HO bond in terminal HPO(-3). The bridging PO(-2) of tripoly-P did not coordinate with aluminum hydroxide. The real-time ATR-FTIR study on condensed phosphate adsorption revealed that a long contact time between condensed phosphates and aluminum hydroxide particles can result in a transformation of an initially formed species into a thermodynamically more stable phase.

Adsorption↗
PubMed2000

Analogues for the molybdenum center of sulfite oxidase: oxomolybdenum(V) complexes with three thiolate sulfur donor atoms.

cis,trans-(L-N2S2)Mo(V)O(SR) [L-N2S2H2 = N,N'-dimethyl-N,N'-bis(mercaptophenyl)ethylenediamine; R = CH2Ph, CH2CH3, and p-C6H4-Y (Y = CF3, Cl, Br, F, H, CH3, CH2CH3, and OCH3)] are the first structurally characterized mononuclear Mo compounds with three thiolate donors, as occurs at the Mo active site in sulfite oxidase. X-ray crystal structures of the cis,trans-(L-N2S2)Mo(V)O(SR) compounds, where R = CH2Ph, CH2CH3, p-C6H4-OCH3, and p-C6H4-CF3, show a similar coordination geometry about the Mo atom with all three sulfur thiolate donors in the equatorial plane. This coordination geometry places two adjacent S ppi orbitals parallel to the Mo=O bond, analogous to the orientation in the ene-dithiolate ligand in sulfite oxidase; the third S ppi orbital lies in the equatorial plane. Charge-transfer transitions from the S p to the Mo d orbitals occur at approximately 28,000 cm(-1) (epsilon: 4,400-6,900 L mol(-1)] cm(-1)) and 15,500 cm(-1) (epsilon: 3,200-4,900 L mol(-1) cm(-1)). The EPR parameters are nearly identical for all the cis,trans-(L-N2S2)Mo(V)O(SR) compounds (g1 approximately 2.022, g2 approximately 1.963, g3 approximately 1.956, Al approximately 58.4 x 10(-4) cm(-1), A2 approximately 23.7 x 10(-4) cm(-1), A3 approximately 22.3 x 10(-4) cm(-1)) and are typical of an oxo-Mo(V) center coordinated by multiple thiolate donors. The g and A tensors are related by a 24 degrees rotation about the coincident g2 and A2 tensor elements, reflecting the approximate Cs coordination symmetry. These EPR parameters more closely mimic those of the low pH form of sulfite oxidase and the "very rapid" species of xanthine oxidase than previous model compounds with two or four thiolate donors. The cis,trans-(L-N2S2)Mo(V)O(SR) compounds undergo a quasi-reversible, one-electron reduction and an irreversible oxidation that show a linear dependence upon the Hammett parameter, sigmap, of the Y group. The cis,trans-(L-N2S2)Mo(V)O(SR) compounds provide a well-defined platform for the systematic investigation of the electronic structures of the Mo(V)OS3 centers and their implications for molybdoenzymes.

Animals↗
PubMed2003

Metallacarbenes from diazoalkanes: an experimental and computational study of the reaction mechanism.

PCP ligand (1,3-bis-[(diisopropyl-phosphanyl)-methyl]-benzene), and PCN ligand ([3-[(di-tert-butyl-phosphanyl)-methyl]-benzyl]-diethyl-amine) based rhodium dinitrogen complexes (1 and 2, respectively) react with phenyl diazomethane at room temperature to give PCP and PCN-Rh carbene complexes (3 and 5, respectively). At low temperature (-70 degrees C), PCP and PCN phenyl diazomethane complexes (4 and 6, respectively) are formed upon addition of phenyl diazomethane to 1 and 2. In these complexes, the diazo moiety is eta(1) coordinated through the terminal nitrogen atom. Decomposition of complexes 4 and 6 at low temperatures leads only to a relatively small amount of the corresponding carbene complexes, the major products of decomposition being the dinitrogen complexes 1 and 2 and stilbene. This and competition experiments (decomposition of 6 in the presence of 1) suggests that phenyl diazomethane can dissociate under the reaction conditions and attack the metal center through the diazo carbon producing a eta(1)-C bound diazo complex. Computational studies based on a two-layer ONIOM model, using the mPW1K exchange-correlation functional and a variety of basis sets for PCP based systems, provide mechanistic insight. In the case of less bulky PCP ligand bearing H-substituents on the phosphines, a variety of mechanisms are possible, including both dissociative and nondissociative pathways. On the other hand, in the case of i-Pr substituents, the eta(1)-C bound diazo complex appears to be a critical intermediate for carbene complex formation, in good agreement with the experimental results. Our results and the analysis of reported data suggest that the outcome of the reaction between a diazoalkane and a late transition metal complex can be anticipated considering steric requirements relevant to eta(1)-C diazo complex formation.

Journal Article↗
PubMed2006

Oxidation of nitrite by a trans-dioxoruthenium(VI) complex: direct evidence for reversible oxygen atom transfer.

Reaction of trans-[Ru(VI)(L)(O)(2)](2+) (1, L = 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane, a tetradentate macrocyclic ligand with N(2)O(2) donor atoms) with nitrite in aqueous solution or in H(2)O/CH(3)CN produces the corresponding (nitrato)oxoruthenium(IV) species, trans-[Ru(IV)(L)(O)(ONO(2))](+) (2), which then undergoes relatively slow aquation to give trans-[Ru(IV)(L)(O)(OH(2))](2+). These processes have been monitored by both ESI/MS and UV/vis spectrophotometry. The structure of trans-[Ru(IV)(L)(O)(ONO(2))](+) (2) has been determined by X-ray crystallography. The ruthenium center adopts a distorted octahedral geometry with the oxo and the nitrato ligands trans to each other. The Ru=O distance is 1.735(3) A, the Ru-ONO(2) distance is 2.163(4) A, and the Ru-O-NO(2) angle is 138.46(35) degrees . Reaction of trans-[Ru(VI)(L)((18)O)(2)](2+) (1-(18)O(2)) with N(16)O(2)(-) in H(2)O/CH(3)CN produces the (18)O-enriched (nitrato)oxoruthenium(IV) species 2-(18)O(2). Analysis of the ESI/MS spectrum of 2-(18)O(2) suggests that scrambling of the (18)O atoms has occurred. A mechanism that involves linkage isomerization of the nitrato ligand and reversible oxygen atom transfer is proposed.

Crystallography, X-Ray↗
PubMed2004

Polymeric silver(I) complexes with pyridyl dithioether ligands: experimental and theoretical investigations on the coordination properties of the ligands.

The reactions of four flexible tetradentate ligands, 1,3-bis(2-pyridylthio)propane (L1), 1,4-bis(2-pyridylthio)butane (L2), 1,5-bis(2-pyridylthio)pentane (L3) and 1,6-bis(2-pyridylthio)hexane (L4) with AgX (X = BF4-, ClO4-, PF6-, or CF3SO3-) lead to the formation of seven new complexes: [AgL1(BF4)]2 (1), [[AgL2](ClO4)]infinity (2), [[AgL2(CH3CN)](PF6)]infinity (3), [[AgL3](BF4)(CHCl3)]2 (4), [[AgL3(CF3SO3)](CH3OH)(0.5)]infinity (5), [[Ag2L4(2)](BF4)2]infinity (6), and [[AgL4](PF6)]infinity (7), which have been characterized by elemental analyses, IR spectroscopy, and X-ray crystallography. Single-crystal X-ray analyses show that complexes 1 and 4 possess dinuclear macrometallacyclic structures, and complexes 2, 3 and 5-7 take chain structures. In all the complexes, the nitrogen atoms of ligands preferentially coordinate to silver atoms to form normal coordination bonds, while the sulfur atoms only show weak interactions with silver atoms and the intermolecular AgS weak contacts connect the low-dimensional complexes into high-dimensional supramolecular networks. Additional weak interactions, such as pi-pi stacking, F...F weak interactions, Ag...O contacts or C-H...O hydrogen bonds, also help to stabilize the crystal structures. It was found that the parity of the -(CH2)n- spacers (n = 3-6) affect the orientation of the two terminal pyridyl rings, thereby significantly influence the framework formations of these complexes. The coordination features of ligands and their conformation changes between free and coordination states have been investigated by DFT calculations.

Crystallography, X-Ray↗
PubMed2003

[Spectra of the complexes of zinc salts with AMP].

The complexes of ZnCl2 and ZnSO4 with AMP in molar ratios of 1:1 and 1:2 were prepared through reflux in alcohol. The compositions of the complexes were determined to be Zn(AMP)2Cl2(A) and Zn(AMP)SO4(B) by chemical and elemental analyses. It was identified via IR analysis for the complexes that nitrogen atom of amino group and one of nitrogen atoms of pyrimidine coordinated to Zn2+ in bidentate fashion. Cl- in the complex of A and SO4(2-) in the complex of B participated in the coordination to Zn2+ and some feedback characteristic was found in the bond of N-->Zn2+, which was proved by XPS spectra. Study on 1H NMR for the complexes showed that two ligands joined the coordination to Zn2+ in the complex of A while one ligand did in the complex of B. Based on the above analyses, the structures of the complexes were presumed.

Adenosine Monophosphate↗
PubMed2002

Studies on 4,7-di-substitution effects of one ligand in [Ru(phen)3]2+ with DFT method.

Studies on the complex [Ru(phen)3]2+ (phen = 1,10-phenanthroline) and its derivatives with 4,7-di-substitution on one ligand(phen) were carried out using the DFT method at the B3LYP/LanL2DZ level of theory. The trends in the substituent effects caused by the electron-pushing group (OH) and the electron-withdrawing group (F), on the electronic structures and the related properties, for example, the energies and the components of some frontier molecular orbitals, the spectroscopy properties, and the net charge populations of some main atoms of the complexes, etc., have been investigated. The computational results show that the substituents have some interesting effects on the electronic structures and the related properties of the complexes. First, according to the analysis of components of LUMO of the complexes, the electron-withdrawing group (F) can activate the main ligand (the substituted ligand, i.e., 2R-phen) and passivate the coligands, on the contrary, the electron-pushing group (OH) can activate the coligands and passivate the main ligand in the first electronic excited states of complexes. Second, both the electron-pushing group (OH) and the electron-withdrawing group (F) can cause a red shift in the electronic ground bands. Third, the characteristics of the atomic net charge populations on the main ligand can also be analyzed in detail by means of a schematic map expressed by several series of arrowheads based on the law of polarity alternation and the idea of polarity interference. The most negative charges are populated on N1, the next most net negative charges are populated on C3 among the skeleton atoms for the three complexes, etc. The computational results can be better used to explain some experimental phenomena and trends.

Intercalating Agents↗
PubMed1998

Structural basis of the chiral selectivity of Pseudomonas cepacia lipase.

To investigate the enantioselectivity of Pseudomonas cepacia lipase, inhibition studies were performed with Sc- and Rc-(Rp,Sp)-1,2-dialkylcarbamoylglycero-3-O-p-nitrophenyl alkylphosphonates of different alkyl chain lengths. P. cepacia lipase was most rapidly inactivated by Rc-(Rp,Sp)-1,2-dioctylcarbamoylglycero-3-O-p-nitrophenyl octylphosphonate (Rc-trioctyl) with an inactivation half-time of 75 min, while that for the Sc-(Rp,Sp)-1,2-dioctylcarbamoylglycero-3-O-p-nitrophenyl octyl-phosphonate (Sc-trioctyl) compound was 530 min. X-ray structures were obtained of P. cepacia lipase after reaction with Rc-trioctyl to 0.29-nm resolution at pH 4 and covalently modified with Rc-(Rp,Sp)-1,2-dibutylcarbamoylglycero-3-O-p-nitrophenyl butyl-phosphonate (Rc-tributyl) to 0.175-nm resolution at pH 8.5. The three-dimensional structures reveal that both triacylglycerol analogues had reacted with the active-site Ser87, forming a covalent complex. The bound phosphorus atom shows the same chirality (Sp) in both complexes despite the use of a racemic (Rp,Sp) mixture at the phosphorus atom of the triacylglycerol analogues. In the structure of Rc-tributyl-complexed P. cepacia lipase, the diacylglycerol moiety has been lost due to an aging reaction, and only the butyl phosphonate remains visible in the electron density. In the Rc-trioctyl complex the complete inhibitor is clearly defined; it adopts a bent tuning fork conformation. Unambiguously, four binding pockets for the triacylglycerol could be detected: an oxyanion hole and three pockets which accommodate the sn-1, sn-2, and sn-3 fatty acid chains. Van der Waals' interactions are the main forces that keep the radyl groups of the triacylglycerol analogue in position and, in addition, a hydrogen bond to the carbonyl oxygen of the sn-2 chain contributes to fixing the position of the inhibitor.

Binding Sites↗