Computer-assisted optimization of an immobilized-enzyme flow-injection system for the determination of glucose

A flow-injection system utilizing the Trinder reaction for the determination of glucose is designed and optimized. Glucose is converted to gluconic acid by passing it through a single-bead-string reactor (SBSR) onto which glucose oxidase enzyme has been immobilized. As it flows through a second SBSR, the gluconic acid reacts with a reagent stream of horseradish peroxidase, 4-aminoantipyrine and 3,5-dichloro-2-hydroxyphenyl sulfonate. The absorbance of the quinoneimine dye produced is then monitored at 510 nm in a flow-through cell. Optimum operating conditions were sought by using both univariate and Composite Modified Simplex procedures. Seven variables were considered. The performance of the system was improved by a factor of 22.5 relative to the starting conditions. A calibration curve obtainedat the optimum conditions was linear for 0–3.3 mM glucose and usable for 0–5.5 mM glucose. The optimization procedures revealed some interesting aspects of the Trinder reaction. scatter diagrams generated from the simplex data showed definite trends for each of the seven variables. These are discussed.     

Charge Movements in the 13-c/s Photocycles of the Bacteriorhodopsin Mutants R82K and R82Q*

We have examined light-induced currents in oriented membranes of the bacteriorhodopsin mutants R82K and R82Q. Our results suggest that two photocurrent components found in R82K, with 30 and 300 us lifetimes, are due to the photocycle of the 13-cis rather than the all-trans form of the pigment. We investigated the pH dependence of these components and their correspondence to absorbance changes at 660 nm characteristic of pho-tointermediates of the 13-cis cycle. The presence of a D₂O effect suggests that the charge motions producing these photocurrents are related to proton or protonated amino acid movement within the molecule. The current amplitudes depend on the protonation states of at least two residues, D85 and (probably) E204. In R82Q, a 10 pis photocurrent is observed that also depends on the protonation state of D85 and is similar to the 30 us current in R82K. We attempt to explain these currents in terms of a model for interacting residues in the extracellular half of the bacteriorhodopsin channel.     

Development of a selective post-column detector for phenols separated by high-performance liquid chromatography

An on-line post-column reactor based on air-segmented continuous flow is described for the determination of phenols. The reaction used is the coupling of diazotized sulfanilic acid with phenols to form highly colored azo dyes. The effect of experimental parameters on the detector response was inveestigated by both univariate and simplex approaches in order to establish optimum reaction conditions. The aqueous reaction system is compatible with common reverse-phase solvents. The detection limit for phneol with the derivatization detector (71 μg 1^?1 shows a 16-fold improvement over u.v. detection of the underivatized phenol. Imprecision, based on multiple injections of sample into the HPLC system and measurement of the peak heights, is ± 0.64% (RSD). The technique is applied to the determination of phenols added to river water and present in residual fuel oil samples.     

15N chemical shifts and long-range 1H-15N coupling pathways of selected strychnos alkaloids

The Strychnos alkaloids have been the focal point of considerable synthetic and spectroscopic effort. We now report the ¹⁵N chemical shifts and long-range ¹H-¹⁵N coupling pathways of strychnine, brucine, and holstiine at natural abundance. Long-range coupling pathways were established using a gradient-enhanced HMQC sequence optimized for the observation of ¹H-¹⁵N long-range couplings.     

PROPERTIES OF SYNTHETIC BACTERIORHODOPSIN PIGMENTS. FURTHER PROBES OF THE CHROMOPHORE BINDING SITE

Abstract— A series of retinals with specific structural alterations have been synthesized to probe the bacteriorhodopsin binding site. The 4-chloro-, 4-bromo- and 4-iodoretinals all form pigments with bacterioopsin but undergo an in situ displacement of the allylic halogen to form the 4-hydroxyretinal pigment. Several naphthyl retinals were prepared which effectively extend the polyene chain and/or add bulk to the ring portion of the chromophore. All the naphthyl retinals form pigments with bacterioopsin but only the pigment containing the derivative with a polyene side chain identical to that of retinal pumps protons efficiently. The 12-butyl-13-desmethylretinal was also synthesized but this analogue did not form a pigment with bacterioopsin. These results confirm the nonspecificity at the ring portion of the chromophore binding site and the importance of the role of the polyene chain in the proton pumping function of bacteriorhodopsin.     

Identification of Photooxidation Sites in Bovine α-Crystallin

Abstract— Because UV irradiation of proteins can produce reactive oxygen species and exposure to UV light has been implicated in cataractogenesis, the sites of photooxidation of bovine α-crystallin, a major lens protein with molecular chaperone activity, were identified using tandem mass spectrometry (MS/MS). Bovine α-crystallin was irradiated with UV light (293 nm) for 1, 4 and 8 h, digested with trypsin and analyzed by matrix-assisted laser de-sorption ionization, time-of-flight mass spectrometry (MALDI) to identify the oxidized sequences. Tryptic peptides were purified by reverse-phase HPLC and oxidized peptides were sequenced by MS/MS to determine the sites of oxidation. Tryptophan fluorescence decreased exponentially with increasing time of UV exposure and peptides containing residues 1-11 of α-crystallin and 1-11, 12-22 and 57-69 of α-crystallin were determined to be oxidized by shifts of 16 D or multiples of 16 Da above the mass of the unmodified peptide. The MALDI analysis revealed single oxidation of all four sequences, which increased with increasing time of UV exposure and possible double oxidation of α 12-22. The specific sites of photooxidation indicate that the N-terminal regions of α-and β-crystallin are exposed to an aqueous environment and are in the vicinity of tryptophan residues from neighboring subunits.     

Quantitation of the effect of hydroxylamine on rhodopsin palmitylation

Rhodopsin (the photosensitive rod visual pigment) has been a model for photobiologic studies of the opsins as well as a structural model for G-protein-coupled receptors. The two palmitate groups attached to cysteines 322 and 323 are thought to serve as membrane anchors for the rhodopsin C-terminus, but the absence of the palmitates does not alter membrane localization. However, removal of the palmitates affects rhodopsin function. Therefore, it is important to quantitate the stability of rhodopsin palmitates to hydroxylamine, which is a widely utilized reagent in biochemical preparations of the apoprotein. We have developed a mass spectrometric method to quantitate the resulting opsin palmitylation. Our data show that both of the bovine rhodopsin palmitates are labile to hydroxylamine, with significant depalmitylation occurring at concentrations of >or=100 mM, with an EC(50) of 220 mM L(-1). The palmitate at position 322 is the more stable to hydroxylamine. Samples prepared in the presence of >50 mM should therefore be considered to be at least partially depalmitylated and the results interpreted accordingly.     

On the Numerical Integration of the Rolling Ball Equations Using Geometrically Exact Algorithms

ABSTRACT

In this paper, new types of numerical integration algorithms developed by the authors are described. The main aim of the algorithms is to numerically integrate differential equations that evolve on geometric objects, such as the rotation group and Euclidean group. The algorithms provide iterates that lie on the prescribed geometric object, either exactly or to some prescribed accuracy, independent of the order of the algorithm. In this sense the algorithms can be called geometrically exact integration algorithms. The paper also describes the application of these new algorithms to the nonholonomic dynamic equations that describe a ball rolling on a flat table, using the kinematic evolution in the Euclidean group.     

Optimal Control and Geodesics on Quadratic Matrix Lie Groups

The purpose of this paper is to extend the symmetric representation of the rigid body equations from the group SO (n) to other groups. These groups are matrix subgroups of the general linear group that are defined by a quadratic matrix identity. Their corresponding Lie algebras include several classical semisimple matrix Lie algebras. The approach is to start with an optimal control problem on these groups that generates geodesics for a left-invariant metric. Earlier work by Bloch, Crouch, Marsden, and Ratiu defines the symmetric representation of the rigid body equations, which is obtained by solving the same optimal control problem in the particular case of the Lie group SO (n). This paper generalizes this symmetric representation to a wider class of matrix groups satisfying a certain quadratic matrix identity. We consider the relationship between this symmetric representation of the generalized rigid body equations and the generalized rigid body equations themselves. A discretization of this symmetric representation is constructed making use of the symmetry, which in turn give rise to numerical algorithms to integrate the generalized rigid body equations for the given class of matrix Lie groups. Dedicated to Professor Arieh Iserles on the Occasion of his Sixtieth Birthday.