Investigating the specific interactions between carbonic anhydrase and a sulfonamide inhibitor by single-molecule force spectroscopy

In this communication, we report on the interaction landscape of an active site-specific enzyme-inhibitor complex by single-molecule force spectroscopy. Electrostatic immobilization was employed to orient a carbonic anhydrase enzyme on a positively charged surface so its active site is pointing upward. This approach to immobilization effectively increases the number of specific interactions measured between the zinc ion of the active site on carbonic anhydrase and a sulfonamide inhibitor tethered to an atomic force microscope (AFM) probe. Further, it reduces the time required for data collection and thereby minimizes the possible mechanical damage to the probe and contamination of the enzyme surface. The rupture force measured at various loading rates is interpreted in terms of a single energy barrier for the carbonic anhydrase enzyme-sulfonamide inhibitor complex from which the kinetic and thermodynamic parameters were estimated on the basis of microscopic models and were compared to the Bell-Evans model. The dissociation rate for the enzyme-inhibitor complex was found to be significantly faster (~35 times) than the natural spontaneous dissociation rate.     

Substituent effects on the amination of racemic allyl carbonates using commercially available chiral rhodium catalysts

In the presence of commercially available chiral rhodium catalysts, a competitive benzylamination of racemic allyl carbonates, substituted with p-X-Ph groups, shows that the reaction proceeds faster with substituents (X) that are more electron-withdrawing. Mechanistic implications of these results are discussed.     

Chaotic Expansion of Elements of the Universal Enveloping Algebra of a Lie Algebra Associated with a Quantum Stochastic Calculus

The functional Ito formula, in the form df() = f( + d ) –f(),is formulated and proved in the context of a Lie algebra L associatedwith a quantum (non-commutative) stochastic calculus. Here fis an element of the universal enveloping algebra U of L, andf() + d() – f() is given a meaning using the coproductstructure of U even though the individual terms of this expressionhave no meaning. The Ito formula is equivalent to a chaoticexpansion formula for f() which is found explicitly. 1991 MathematicsSubject Classification: primary 81S25; secondary 60H05; tertiary18B25.     

Photoelectron spectroscopy of carbonyls. Bicyclo[2.2.1]-heptane-2,3-diones and bicyclo [2.2.1] hept-5-ene-2,3-diones

The HeI photoelectron spectra (UPS) of several bicyclo [2.2.1] heptane-2,3-diones and bicyclo[2.2.1] hept-5-ene-2,3-diones are presented. Interpretations are based on CNDO/s computations and empirical correlations. The n₊ orbital of the two carbonyl groups interacts strongly with, the π orbital of the 5-ene moiety in bicyclo[2.2.1]hept-5-ene-2,3-diones. This interaction is dominantly “through-bond”, there being little or no direct (i.e. “through-space”) overlap. The net result is that insertion of 5-ene unsaturation increases the splitting of the n₊ and n_? orbitals from ca. 1.9 to ca. 2.4 eV. Finally, the π* (CO) ← n₊ electronic absorption spectra of the [5-ene] -compounds, which are geometrically suited to an investigation of π/π* (CO) interactions, suggest that such mixing is negligible.     

Scintillator characterization using the LBL pulsed X-ray facility

We have developed a bench-top pulsed X-ray system for measuring scintillation properties of compounds in crystalline or powdered form. The source is a light-excited X-ray tube that produces 40 X-ray photons (mean energy 18.5 keV) per steradian in each 100 pps fwhm pulse. The repetition rate is adjustable from 0 to 10⁷ pulses per second. The fluorescent emanations from the X-ray excited samples are detected with either a sapphire-windowed microchannel plate photomultiplier tube (spectral range 150–650 nm, transit time jitter 40 ps fwhm) or a quartz-windowed GaAs(Cs) photomultiplier tube (spectral range 160–930 nm, transit time jitter 4 ns fwhm). Decay curves are acquired using a TDC having 40 ps fwhm resolution over an 84 ms dynamic range. A computer controlled monochromator can be inserted into the optical path to measure the emission spectrum or wavelength resolved decay time. A computer-controlled sample changer allows up to 64 samples to be measured without intervention.     

Estimating kinetic and thermodynamic parameters from single molecule enzyme-inhibitor interactions

We report the application of recently developed microscopic models to estimate the apparent kinetic and thermodynamic parameters in a single molecule force spectroscopy study of the carbonic anhydrase enzyme and a complementary sulfonamide inhibitor. The most probable rupture force for the enzyme-inhibitor interaction shows a nonlinear dependency on the log-loading rate. Estimates for the kinetic and thermodynamic parameters were obtained by fitting the nonlinear dependency to linear cubic potential and cusp potential models and compared to the standard Bell-Evans model. The reliability of the estimated parameters was verified by modeling the experimental rupture force distributions by the theoretically predicted distributions at rupture. We also report that linkers that are attached to the enzyme and inhibitor show appreciable effects on the apparent kinetic and thermodynamic parameters.