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R Shrager

Publications and source records attributed to R Shrager.

8 recordsLinked to original sources
PubMed1996

KINFIT II: a nonlinear least-squares program for analysis of kinetic binding data.

We describe a versatile computer program for least-squares fitting of ligand/receptor association and dissociation curves from several experiments simultaneously. The program is designed to handle any number of classes of binding sites reacting with a single ligand that may have two forms: labeled and unlabeled. For a single class of binding sites, the exact, analytical solution is used to generate the computed curves. For more than one class of sites, the computed curves are generated through numerical solution of a set of ordinary differential equations. The parameters determined with this procedure are the on- and off-rate constants and the concentrations of each binding site class. An extensive selection of experimental designs can be processed. The times of observation may be freely chosen, although that choice will affect the quality of the results. Starting with a sample material (e.g., cells, membranes, macromolecules), one can preincubate (to equilibrium) with any combination of labeled and unlabeled ligand. One can then perturb the system by adding any combination of labeled and cold ligand or simply diluting the sample; such an experiment can be continued through several perturbations. A variety of such runs may be combined for analysis as a single data set.

Kinetics↗
PubMed1993

Reversal of caldesmon binding to myosin with calcium-calmodulin or by phosphorylating caldesmon.

Caldesmon, an actin-binding protein from smooth muscle and non-muscle cells, has previously been shown to bind stoichiometrically to smooth muscle myosin in an ATP-dependent manner. We now show quantitatively the effects of Ca(2+)-calmodulin and phosphorylation on the binding of caldesmon to myosin. Ca(2+)-calmodulin reduces the binding of caldesmon to myosin with the same effectiveness as it does the binding of caldesmon to actin. However, Ca(2+)-calmodulin is ineffective in antagonizing the binding of the purified myosin-binding region of caldesmon to myosin. These and other results suggest that Ca(2+)-calmodulin binding to the COOH-terminal region of caldesmon is responsible for reversal of binding to myosin. Phosphorylation of the NH2-terminal region of caldesmon by the co-purifying kinase, calmodulin-dependent protein kinase II, weakens but does not eliminate the binding of caldesmon to smooth muscle myosin. Finally, phosphorylation of smooth muscle myosin by smooth muscle myosin light chain kinase has no effect on the binding of caldesmon to myosin. Since Ca(2+)-calmodulin and phosphorylation of caldesmon weaken the binding of caldesmon to both actin and myosin, these events may be coordinately regulated.

Adenosine Triphosphate↗
PubMed1988

Optimal two-stage designs for clinical trials with binary response.

We present a simple two-stage design for a randomized clinical trial with dichotomous outcomes. It is based on a design of Ellenberg and Eisenberger which permits early acceptance of the null hypothesis after the first stage. We have optimized the design by minimizing the average expected sample size subject to constraints on the type 1 and type 2 errors. The resulting designs have maximum sample size only slightly larger than that of single stage trial, with 40-45 per cent of this maximum allocated to the first stage, and null hypothesis probability of early acceptance in excess of 0.60.

Clinical Trials as Topic↗
PubMed1977

A model for the kinetics of distribution of actinomycin-D in the beagle dog.

A pharmacokinetic model is presented for the distribution of actinomycin-D in the beagle dog. A simple, flow-limited model provides good simulations of the data at doses of 0.6 mg/m2 (0.03 mg/kg) and 2.7 mg/m2 (0.135 mg/kg) for most normal tissues. This implies that uptake of actinomycin-D in vivo is limited by tissue blood flow rate rather than by cell permeability. However, uptake by the testes is restricted by a blood-testis barrier, and a linear membrane-limited model is required to simulate the testis data. Linear binding of actinomycin-D to tissue is suggested by the fact that tissue concentrations are proportional to dose at least up to the lethal dose in dogs. The binding is also rapid and reversible as indicated by the tissue concentration curves which are parallel to the time course of the declining plasma curves.

Animals↗
PubMed1975

Integrated steady state rate equations and the determination of individual rate constants.

Integrated steady state rate equations have been used to determine the kinetic constants (Vs, Ks, Vp, and Kp) and rate constants (k1, k2, k3, and k4) of the reversible enzyme mechanism: (see article). The fumarase reaction has been used as a model to illustrate the procedures for determining these constants. In contrast to initial velocity studies, the values of the constants have been obtained by examining the enzyme reaction in only one direction rather than in both forward and reverse directions. To accomplish this, a new procedure is described for fitting data to integrated rate equations which eliminates problems encountered when data are analyzed graphically. The advantages of examining on enzyme reaction in one direction with these new procedures allow this method to be extended to the examination of enzymes with simple mechanisms where initial velocities are difficult to measure because either the substrate or product is not readily available, or because the reaction is not readily reversible.

Animals↗
PubMed1972

Quantitative studies of the delivery of hepatic-synthesized bilirubin to plasma utilizing -aminolevulinic acid-4- 14 C and bilirubin- 3 H in man.

After the simultaneous intravenous administration of unconjugated bilirubin-(3)H and delta-aminolevulinic acid-4-(14)C, the plasma disappearance curves of unconjugated bilirubin-(3)H and the plasma appearance curves of biosynthesized unconjugated bilirubin-(14)C have been defined in seven patients, three of whom had acute intermittent porphyria (AIP). The incorporation of (14)C into plasma unconjugated bilirubin, derived by an analysis which involves deconvolution of the two plasma curves, varied between 13.1 and 23.5% (mean 19.3%) of the injected dose in the nonporphyric patients and between 5.4 and 13.6% (mean 8.3%) of the injected dose in the porphyric patients. In five of the patients, the stercobilin-(14)C specific activity in a pooled specimen of feces was measured, enabling the following further values to be calculated: (a) the total (14)C radioactivity incorporated into bilirubin (21.0 and 25.3% [mean 23.2%] of the injected dose in two of the nonporphyric patients and between 8.5 and 25.3% [mean 14.2%] of the injected dose in the porphyric patients), and (b) the proportion of hepatic synthesized bilirubin delivered directly to plasma in the unconjugated form (between 0.520 and 0.904; mean for nonporphyric patients 0.712; mean for porphyric patients 0.614). The results demonstrate that a large proportion of bilirubin derived from hepatic hemes passes through the plasma in the unconjugated form before conjugation and secretion into bile.

Adult↗