Dual wavelength/split beam spectrophotometry: computer acquisition of absorbance spectra.

The adaptation of a commercially available dual wavelength/split beam spectrophotometer for the real time acquisition by a minicomputer of absorbance spectra is described. The computer software and interface are designed so that: a) The normal operation of the spectrophotometer is unaltered; b) the adaptation of the spectrophotometer for computer acquisition of spectra is relatively simple and only a rudimentary knowledge of electronics and computer programming is required.The utility of this adaptation of a dual wavelength/split beam spectrophotometer for baseline correction, enhancement of the sensitivity of the spectrophotometer and subsequent analysis of recorded absorbance spectra is described.     

The reaction between ferrous polyaminocarboxylate complexes and hydrogen peroxide: an investigation of the reaction intermediates by stopped flow spectrophotometry

The reactions of Fe(II)EDTA, Fe(II)DTPA, and Fe(II)HEDTA with hydrogen peroxide near neutral pH have been investigated. All these reactions have been assumed to proceed through an active intermediate, I1, (Formula: see text) where pac is one of the three polyaminocarboxylates mentioned above. I1, whether .OH radical or an iron complex, reacts with ethanol, formate, and other scavengers at rates relative to k2 that, with the exception of t-butanol and benzoate, are similar, but not identical, to those expected for the.OH radical. In contrast, at pH 3, in the absence of ligands the reaction of I1 with Fe2+ was inhibited by ethanol and t-butanol and the reactivity of I1 towards these two scavengers relative to ferrous ion is identical to that exhibited by the hydroxyl radical. When pac = HEDTA, the intermediate of the first reaction reacts with formate ion to form the ferrous HEDTA ligand radical complex, which is characterized by absorption maxima at 295 nm (epsilon = 2,640 M-1 cm-1) and 420 nm (epsilon = 620 M-1 cm-1). For the reaction of Fe(II)HEDTA with H2O2, the following mechanism is proposed: (Formula: see text) where k17 = 4.2 X 10(4) M-1 sec-1 and k19 = 5 +/- 0.2 sec-1.     

Kinetics of reduction of purified liver microsomal cytochrome P-450 in the reconstituted enzyme system studied by stopped flow spectrophotometry.

Stopped flow studies were undertaken to examine the kinetics of reduction of 5,6-benzoflavone-inducible P-450 LM4 by NADPH in the presence of NADPH-cytochrome P-450 reductase and phospholipid under anaerobic CO at 25 degrees C. The reaction exhibited biphasic kinetics irrespective of NADPH concentration or of the molar ratio of reductase to P-450 LM4. The apparent first order rate constants for the fast and slow phases were determined to be 0.9 to 1.0 and 0.25 s-1, respectively. With the reductase and P-450 LM4 present in equimolar amounts, the total amount of P-450 LM4 reduced increased linearly with NADPH concentration; the titration gave a stoichiometry of 2 mol of NADPH per mol of reductase-cytochrome complex. The NADPH concentration had no appreciable effect on the magnitude of the first order rate constants for the fast and slow phases. The kinetics obtained in the presence of benzphetamine were essentially indistinguishable from those seen in the absence of this substrate, while the amount of P-450 LM4 reduced in the fast phase, but not the rate constant for this phase, decreased when phospholipid was omitted from the reaction mixture. Nearly maximal rates of NADPH oxidation by P-450 LM2 OR LM4 were obtained with a molar ratio of reductase to P-450 LM of 1.0. Benzphetamine enhanced the oxidation of NADPH by P-450 LM2 but had no effect on the activity of P-450 LM4. Rates of NADPH oxidation in the presence of P-450 LM2 and LM4 decreased by 80 and 40%, respectively, when phospholipid was omitted from the reconstituted enzyme system. These studies provide evidence for the formation of a catalytically functional 1:1 complex between the reductase and P-450 LM4, and indicate that P-450 LM2 and LM4 differ in their dependence on phospholipid.     

Multiwavelength analysis of the aldehyde hydration of pyridoxal phosphate: A stopped flow study

A simple method has been devised to determine the rate constants of the aldehyde hydration of pyridoxal-P by coupling the hydration reaction to the formation of a Schiff base derived from free pyridoxal-P and a primary amine present in excess. The primary amine component to be chosen should have a pK value very close to the pH at which the hydration ratio is to be determined. At pH 7.8 glycine ethyl ester is particularly well suited as primary amine component due to its favorable pK of 7.83. The overall reaction consisting of two independent reaction steps was monitored at different wavelengths and analyzed by means of the formal integration method. The rate constant of the forward reaction (k_h¹ = k_h [H₂O]) and of the reverse reaction (k_d) were found to be 1.99 s^?1 and 8.09 s^?1, respectively. The corresponding equilibrium constant is 0.25.     

One-dimensional computer analysis of oscillatory flow in rigid tubes.

The dynamic characteristics of catheter-transducer systems using rigid tubes with compliance lumped in the transducer and oscillatory flow of fluid in rigid tubes were analyzed. A digital computer model based on one dimensional laminar oscillatory flow was developed and verified by exact solution of the Navier-Stokes Equation. Experimental results indicated that the damping ratio and resistance is much higher at higher frequencies of oscillation than predicted by the one dimensional model. An empirical correction factor was developed and incorporated into the computer model to correct the model to the experimental data. Amplitude of oscillation was found to have no effect on damping ratio so it was concluded that the increased damping ratio and resistance at higher frequencies was not due to turbulence but to two dimensional flow effects. Graphs and equations were developed to calculate damping ratio and undamped natural frequency of a catheter-transducer system from system parameters. Graphs and equations were also developed to calculate resistance and inertance for oscillatory flow in rigid tubes from system parameters and frequency of oscillation.     

Fluorescence stopped flow analysis of the interaction of virginiamycin components and erythromycin with bacterial ribosomes

The kinetics of the interaction between the 50 S subunits (R) of bacterial ribosomes and the antibiotics virginiamycin S (VS), virginiamycin M (VM), and erythromycin have been studied by stopped flow fluorimetric analysis, based on the enhancement of VS fluorescence upon its binding to the 50 S ribosomal subunit. Virginiamycin components M and S exhibit a synergistic effect in vivo, which is characterized in vitro by a 5- to 10-fold increase of the affinity of ribosomes for VS, and by the loss of the ability of erythromycin to displace VS subsequent to the conformational change (from R to R*) produced by transient contact of ribosomes with VM. Our kinetic studies show that the VM-induced increase of the ribosomal affinity for VS (K*VS = 25 X 10(6) M-1 instead of KVS = 5.5 X 10(6) M-1) is due to a decrease of the dissociation rate constant (k*-VS = 0.008 s-1 instead of 0.04 s-1). The association rate constant remains practically the same (k+VS approximately k*+VS = 2.8 X 10(5) M-1 s-1), irrespective of the presence of VM. VS and erythromycin bind competitively to ribosomes. This effect has been exploited to determine the dissociation rate constant of VS directly by displacement experiments from VS . 50 S complexes, and the association rate constant of erythromycin (k+Ery = 3.2 X 10(5) M-1 S-1) on the basis of competition experiments for binding of free erythromycin and VS to ribosomes. By making use of the change in competition behavior of erythromycin and VS, after interaction of ribosomes with VM, the conformational change induced by VM has been explored. Within the experimentally available concentration region, the catalytic effect of VM has been shown to be coupled to its binding kinetics, and the association rate constant of VM has been determined (k+VM = 1.4 X 10(4) M-1 S-1). Evidence is presented for a low affinity binding of erythromycin (K*Ery approximately 3.3 X 10(4) M-1) to ribosomes altered by contact with VM. A model involving a sequence of 5 reactions has been proposed to explain the replacement of ribosome-bound erythromycin by VS upon contact of 50 S subunits with VM.     

Characteristics of a 1:30 mixing ratio stopped flow apparatus

The annular mixer of a small stopped flow apparatus for following changes in transmission is presented together with test results on mixing NaOH with ferricytochromec in the volume ratio 130.This work was supported in part by the Chicago and Illinois Heart Associations (C70-66) and by the National Science Foundation (GB-28023)     

Evaluation of breast carcinoma chemosensitivity by flow cytometric DNA analysis and computer assisted image analysis.

Flow cytometric (FCM) DNA and S-Phase (S%) analyses were compared to computerized image analysis (SAMBA 2005) in 27 breast carcinomas (T3, N0-N1, M0) treated by 3 cycles of preoperative Adriamycin, vincristine, cyclophosphamide, methotrexate, 5-fluorouracil (AVCMF) chemotherapy (CT). Twelve carcinomas had shown objective regression and 15 no regression. Samples studied were obtained by sequential fine-needle cytopunctures. Comparing DNA profiles obtained by both methods before and after the first cycle, it appears that tumors can be divided into 3 groups. In the first group (10 cases), no changes were observed after the first cycle of CT. These tumors before treatment had either single DNA peak without cells in S% and G2M or a major peak with a small S% and G2M peak. The second group (9 cases) showed some changes in DNA profiles with an increased G2M peak but no additional values; these tumors before treatment had a small S% and a G2M peak. In the third group (8 cases), before treatment, all were non-diploid with high S% and high G2M. After the first cycle, all showed obvious changes in DNA profiles with a decrease of the G0/G1 peak and an increased S% and G2M with dispersed additional values along the scale in (G2M) x 2 and (G2M) x 4 regions. When changes were compared to tumor regression in the 1st and 2nd groups, 1/10 and 3/9 cases, respectively, were evaluated as objective regression. In the third group, all had objective regression (p less than 0.001). In most cases, a good correlation was observed with both methods.(ABSTRACT TRUNCATED AT 250 WORDS)     

Dual wavelength imaging allows analysis of membrane fusion of influenza virus inside cells

Influenza virus hemagglutinin (HA) is a determinant of virus infectivity. Therefore, it is important to determine whether HA of a new influenza virus, which can potentially cause pandemics, is functional against human cells. The novel imaging technique reported here allows rapid analysis of HA function by visualizing viral fusion inside cells. This imaging was designed to detect fusion changing the spectrum of the fluorescence-labeled virus. Using this imaging, we detected the fusion between a virus and a very small endosome that could not be detected previously, indicating that the imaging allows highly sensitive detection of viral fusion.     

NaCl-induced chromatin condensation. Application of static light scattering at 90 degrees and stopped flow technique

We have studied the NaCl-induced condensation of calf thymus chromatin by static light scattering of 90 degrees and shown that the increase in NaCl concentration up to 120-170 mM results in a large increase in scattering intensity of the total chromatin. Histones H1-depleted and trypsinized chromatin preparations do not reveal such a large increase in scattering intensity. The increase in the scattering intensity reflects the folding of the chromatin filaments, but not their aggregation. We have used this effect to monitor the kinetics of the chromatin condensation in response to a jump to higher NaCl concentrations by means of a stopped-flow technique. The results show that the condensation is a fast complex process consisting of at least two steps. The first step is only partially resolved by the stopped-flow apparatus. The second step has a time constant in the range of 20-50 ms, which does not depend on chromatin concentration.     

Benzoxazinone derivatives: new fluorescent probes for two-color flow cytometry analysis using one excitation wavelength

A new class of fluorescent dye which upon excitation at 488 nm turns red is shown to be probe-suitable for using in flow cytometry alone or in conjunction with fluorescein derivatives. 7-dimethylamino 3-(p-formylstyryl) 1,4 benzoxazin 2-one is suitable for rendering microorganisms, such as Plasmodium merozoites and cells detectable by flow cytometry, allowing a dual fluorescence analysis when the cells are labelled with suitable fluoresceinylated ligands such as fluorescein labeled neoglycoproteins or antibodies. The synthesis of the new benzoxazinone derivatives is described: p-[beta-(7-dimethylamino 1,4 benzoxazin 2-one 3-yl)-vinyl]-phenylpropenoic acid can be easily activated as a hydroxysuccinimide derivative and linked to amino groups of polypeptides. Hydrophilic polypeptides such as poly-L-lysine or glycosylated polymers combined with this new fluorescent dye are shown to be helpful in analyzing cell surface receptors, in dual fluorescence flow cytometry analysis, using a single excitation wavelength and two sets of compounds labeled with the new benzoxazinone derivative and with fluorescein isothiocyanate, respectively. The new benzoxazinone derivative has a high molar absorbance, a good quantum yield fluorescence when it is bound to hydrophilic polypeptides and its fluorescence intensity is not dependent on pH in the physiological pH range.     

A stopped flow transient kinetic analysis of substrate binding and catalysis in Escherichia coli D-3-phosphoglycerate dehydrogenase

Pre-steady state, stopped flow analysis of Escherichia coli D-3-phosphoglycerate dehydrogenase was performed by following the fluorescence of protein tryptophan and the fluorescence resonance energy transfer from protein tryptophan to bound NADH. The results indicate that binding of substrates is ordered, with coenzyme, NADH, binding first. Furthermore, the analysis indicated that there are two sets of sites on the tetrameric enzyme that can be differentiated by their kinetic behavior. NADH binding was consistent with an initial binding event followed by a slow conformational change for each site. The slow conformational change is responsible for the apparent tight binding of NADH to the apoenzyme but is too slow to participate in the catalytic cycle when the enzyme is rapidly turning over. Subsequent binding of the substrate, alpha-ketoglutarate, was characterized by a rapid equilibrium binding event followed by a conformational change for each site. Catalysis in the direction of NAD(+) reduction showed a distinct burst of activity followed by a slow rate of turnover, indicating that the rate-limiting step is after hydride transfer. Catalysis in the direction of NADH oxidation did not display burst kinetics, indicating that the rate-limiting step is at or before the hydride transfer step. The burst data indicated that the rate of NAD(+) reduction (3.8 s(-1)) is similar to the k(cat) of the enzyme (2-3 s(-1)) in that direction. However, analysis of the reaction with deuterated NADH failed to show an effect on the velocity of the reaction with a V(H)/V(D)=1.07+/-0.06. None of the other rates determined by stopped flow analysis could account for the k(cat) of the enzyme in either direction (forward k(cat)=0.01 s(-1), reverse k(cat)=2-3 s(-1)), suggesting that the rate-limiting step in both directions is a conformational change in the enzyme that is not detected optically.     

The carbamate reaction of glycylglycine, plasma, and tissue extracts evaluated by a pH stopped flow apparatus.

We have used a stopped flow rapid reaction pH apparatus to investigate the carbamate equilibrium in glycylglycine solutions and in three biological tissues, human plasma, sheep muscle, and sheep brain, as well as to investigate the kinetics of carbamate formation in glyclyglycine solution and in human plasma. The rapid reaction apparatus was equipped with a pH sensitive glass electrode in order to follow the time course of pH from 0.005 to 100 s after rapid mixing of a solution of amine or protein and CO2. Two phases of the pH curve were observed: a fast phase representing carbamate formation, and a slow phase due to the hydration of CO2 which was uncatalyzed since a carbonic anhydrase inhibitor was added to the biological solutions. From the time course of pH change during the fast phase K2, the R-NH2 ionization constant, and Kc, the carbamate equilibrium constant as well as the velocity constant for the formation of carbamate, ka could be calculated from data at different pH and pCO2. The carbamate formed in glycylglycine solutions over a wide range of pH and pCO2 was found consistent with the theory of carbamate formation and with published data. At ionic strength 0.16 and 37 degrees pK is 7.67. pKc 4.58. The heat of the carbamate reaction (deltaH) was calculated to be -3.2 kcal/mol between 20 degrees and 37 degrees. Kt of glycylglycine depends quantitatively on ionic strength as predicted by the Debye-Huckel theory. With ionic strength 0.16 ku was found to be 2,500 M1 S1 at 37 degrees. The activation energy of carbamate formation is 6.7 kcal/mol. Carbamate measurements in human plasma at pCO2 from 38 to 359 Torr. pH from 6.9 to 8.3, temperature 37 degrees, and ionic strength 0.15 provided evidence that two kinds of amino groups participate in carbamate formation. From the equilibrium constants computed for the two species they could be identified as alpha- and epsilon-amino groups. On the basis of a protein molecular weight of 69.000. 0.6 alpha-amino groups/molecule with pKz=7.0 and pKc=4.2, and 5.9 epsilon-amino groups/molecule with pKz=9.0 and pKc=4.3 contribute to carbamate formation. The velocity constant ka was estimated to be 4,950 M1 S1 for the alpha-amino groups and 13,800 M1 S1 for the epsilon-amino groups. Under physiological conditions (pCO2=40 Torr. pH=7.4). The concentration of carbamate in plasma is 0.6 mM and the half-time of carbamate formation is 0.05 s. In extracts prepared from sheep brain at 37 degrees pH=7 and pCO2=35 Torr. the carbamate formation was estimated to be 0.8 mM. With pCO2=70 Torr and the same pH and temperature the carbamate concentration in muscle approximates 0.3 mM and increases to 7 mM as pH rises to 8. It is concluded that, as in plasma, a considerable number of epsilon-amino groups appear to be available for carbamate formation in these tissues.