Cytogenetic studies of three triazine herbicides. I. In vitro studies

Atrazine, simazine, and cyanazine are widely used pre-emergence and post-emergence triazine herbicides that have made their way into the potable water supply of many agricultural communities. Because of this and the prevalence of contradictory cytogenetic studies in the literature on atrazine, simazine, and cyanazine, a series of in vitro experiments was performed to investigate the ability of these three triazines to induce sister chromatid exchanges (SCEs) and chromosome aberrations (CAs) in human lymphocyte cultures. Our results showed that all three triazines failed to produce any significant increases in SCEs or CAs up to the limits of solubility [using 0.5% dimethyl sulfoxide (DMSO)]. Our results are discussed in light of contradictory results in the literature.     

Significance of retrospective studies.

Examples of retrospective studies are presented to demonstrate some facets of such studies, both good and bad, pointing out the need for good controls. Also important are a clear idea of the question to be answered, and careful planning around that answer as the study progresses.     

Biopharmaceutical studies of spirobishexahydropyrimidine.

Oral administration of spirobishexahydropyrimidine showed an increase in the activity of serum transaminases, lactate dehydrogenase and alkaline phosphatase. Biological half life and other pharmacokinetic parameters showed rapid absorption and slow elimination of the drug.     

Spin-label studies of tropomyosin.

Studies are reported on nitroxide spin-labeled tropomyosin. The labels attach to sulfhydryl groups and to amino groups. The amino spins are highly mobile, the sulfhydryl much less so. Spin count studies show an average of approximately 0.5 labeled sulfhydryl/tropomyosin molecule and only approximately 0.15 labeled amino group/molecule. The spectra are used tostudy the denaturation of tropomyosin by guanidine hydrochloride. The information obtained reveals the course of denaturation at sites near the sulfhydryl group. It is found that these sites are more susceptible to guanidine than the bulk of the molecule; denaturation at the sulfhydryl sites is complete by 1.5 M guanidine, whereas optical studies indicate the molecule as a whole is not completely denatured until the concentration reaches 3.5 M. Spectra are also shown of tropomyosin fibers oriented variously with respect to the applied magnetic field. Strong orientation effects are seen and these indicate that the sulfhydryl-attached spins (but not the amino-attached spins) have a definite orientation in the fiber. Interpretation of the spectra reveals that the normal to the nitroxide plane is inclined to the fiber axis at an angle of 50 degrees. Circular dichroism studies in the tyrosine region also reveal drastic changes with guanidine denaturation, confirming the idea that denaturation produces pronounced increase in mobility at the beta carbon (as in the sulfhydryl casey). A strong negative band existing only in helical tropomyosin at pH's where the tyrosines are uncharged appears to be due to interaction of tyrosines with the helical backbone, whereas the appearance of a strong positive CD band at 250 nm at high pH (approximately11) seems to be ascribable to interaction between the charged phenolic groups and the dissymmetric backbone alpha-carbon atom.     

Genetical studies onOenothera. V.

Molecular Genetics and Genomics -     

Chicken fumarase. II. Kinetic studies.

The catalysis of the hydration of fumarate and deshydration of L - malate by chicken fumarase was measured spectrophotometrically over a range of substrate concentrations from 4 times 10(-3) M to 8 times 10(-5) M for fumarate and from 8 times 10(-2) M to 10(-3) M for L - malate. For the forward and reverse reactions, linear Lineweaver and Burk plots were obtained. The Michaelis constants and the maximum initial velocities for both substrates were determined and the Haldane relation was found to be obeyed. The effect of pH on activity was investigated over a pH range from 5.5 to 9.0 and the data indicate the presence, in the active site, of two ionizable groups, one in the acidic form and one in the basic form. The values of the ionization constants, determined for the enzyme - substrate complexes, agree closely with the ones obtained for the porcine enzyme. The mode of action of twenty-four structural analogs on the initial velocity of the dehydration of L-malate, by chicken fumarase was examined. From these studies, two regions positively charged appear necessary for the effective binding of the carboxylates of the substrates and competitive inhibitors to the active center. Moreover, the data suggest the presence of an additional group, in the catalytic site of chicken fumarase, that stabilizes the carbon-carbon double bond common to fumarate and its structural analogs. Finally, from the comparison of the kinetic properties of the chicken and pig fumarases, it may be concluded that the catalytic mechanism of the homologous enzymes are very similar, if not identical.     

Conformational studies of polymers and copolymers of L-aspartate esters. I. Preparation and solution studies

An alcoholysis method is described for the modification of high molecular weight poly(β-benzyl L -asparatate); by this method the benzyl groups in the polypeptide have been replaced by methyl, ethyl, isopropyl, n-propyl, and phenethyl groups to give a series of copolymers of each of the corresponding aspartate esters with benzyl L -aspartate. By repeating the reactions, replacement of better than 99% has been achieved in some cases to give in effect the homopolymer. Optical rotatory dispersion studies show that of all the systems studied only poly(β-methyl L -aspartate) has the left-handed helix sense, the others are right-handed. It is shown further that the helix sense is not an intrinsic property of the nature of the aspartate side chain. Raising the temperature of chloroform solutions of the right-handed form of the copolymers of benzyl L -aspartate and ethyl L -aspartate results in a transition to the left-handed helix, the temperature of the transition being dependent on the composition of the copolymer. Also poly(β-n-propyl L -aspartate) undergoes a transition from the right- to the left-handed helix form at 59°C. These results suggest a general pattern of behavior of poly(aspartate esters) and that with suitable conditions of solvent and temperature they may be in either the right- or left-handed helical form.