Dan F. Bradley

Aggregation of cationic dyes on acid polysaccharides I. Spectrophotometric titration with acridine orange and other metachromatic dyes

Abstract The spectrophotometric titrations of various classes of acid polysaccharides (polycarboxylates, polysulfates, mucopolysaccharides and heparinoids) in dilute solution using four metachromatic dyes are described. Acridine orange was found to be applicable for quantitative analysis in all four groups of polymers. The equivalent weights obtained with this dye using about 25 μg of polymer were within 1–8% of the values obtained by other analytical methods. Methylene blue was found to be applicable for polymers where at least one negative site occurs regularly per sugar ring. Proflavine gave quantitative titrations with highly charged polymers and neutral red with polymers of relatively low charge density. Titration curves with methylene blue and proflavine also provide a spectrophometric means of distinguishing between acidic polymers with relatively homogeneous and non-homogeneous charge distributions.

Inhibition of histamine methyltransferase by serotonin and chlorpromazine derivatives: electronic aspects.

Summary The kinetics of inhibition of histamine methyltransferase (S-adenosylmethio-nine:histamine N-methyltransferase, EC 2.1.1.8) by serotonin, chlorpromazine and a number of their derivatives has been investigated. Lineweaver-Burk plots showed that these compounds act as non-competitive inhibitors with Ki values ranging from 13 to 130 μM. Dialysis experiments showed the inhibition to be kinetically reversible. The electronic nature of the complex formed between enzyme and inhibitor has been investigated by molecular-orbital calculations of selected reactivity indices of these two groups of compounds. The principal characteristic of the electronic configuration of these compounds which appears to determine their relative Ki values is their ability to donate electrons, as measured by the energy of their highest filled molecular orbitals. It is suggested, on the basis of the data presented, that the formation of the enzyme-inhibitor complex involves partial or total transfer of one or more electrons from the inhibitor to the enzyme.

Binding of dyes to polycations I. Biebrich scarlet and histone interaction parameters

Abstract Spectroscopic studies indicate that the anionic dye Biebrich scarlet binds and stacks to polycations in an analogous way to cationic dyes on polyanions. Both exciton and dispersion interactions are needed to account for the spectral shifts and intensity changes. The low stacking coefficients are suggestive but not strong evidence for helical structure in the polycations examined. Calculations based on exciton theory using the observed spectral shifts, show that the dyes lie on the outside of the polymers, probably in a radial orientation.

Metachromatic reaction of proflavine bound to DNA and RNA. Spectrophotometric titration and quantitative optical parameters

Experimental conditions were determined under which spectral changes in proflavine due to binding to nucleic acids can be quantitatively analyzed by starting with the maximally-saturated complex (1 dye per phosphate group) and keeping the amount of bound dye constant (negligible free dye) as the number of sites is increased. Calculation of various optical parameters shows that both a blue shift in frequency and decrease in oscillator strength occur in the spectra of 1- to-1 complexes of proflavine with native and denatured DNA and RNA, and that the extent of hypochromism is greater for denatured DNA and RNA than for native DNA. At ratios of sites-to-dye (P/D) greater than one, the red-shifted spectrum of the “strong-binding” complexes appears. The redistribution of dyes on excess sites is similar for denatured and native DNA up to P/D= 5. However, quantitative and qualitative differences in the spectra of these complexes occur at higher P/D. The data emphasize the multiplicity in geometry of binding, discussed by others in regard to native DNA, and elucidate the origin of several features of the induced optical activity of proflavine in these complexes.

Reconstruction of protein and nucleic acid sequences: IV. The algebra of free monoids and the fragmentation stratagem

The problem of determining the sequence of a biopolymer from its fragments is stated in mathematical terms. Using concrete properties of a free monoid, certain general classes of biopolymers are shown to be insolvable from fragment data produced by complete digestion where enzymes specific for any possible combination of chemical bonds are employed.