Dihydrofolate reductase (DHFR) was measured during the development in rats of brain tumors induced following inoculation with avian sarcoma virus. Increasing activity of this enzyme in brain was correlated with the course of primary brain tumor growth. The specific activities of DHFR in primary human brain tumor tissues were comparable to those found in avian sarcoma virus-induced brain tumors ...

The binding of thionine (3,6-diaminophenothiazine) to trypsin is associated with a red shift in the visible absorption spectrum of the dye. Spectrophotometric titration and equilibrium dialysis measurements are consistent with the presence of a single thionine-binding site on the trypsin molecule. At pH 7 and 4O, &is8 for the trypsin-thionine complex is 1.2 X lOUs M. The dye is displaced from t...

The interaction of ribonuclease A with cupric and zinc ions has been studied spectrophotometrically and by potentiometric titration in the presence and absence of cytidylic acid derivatives. In the absence of cytidylic acid, the results suggest that each cupric ion distributes among a set of approximately four spectrally similar sites; each site appears to consist mainly of a single imidazole s...

Kinetic measurements in the pH range 7.0 to 9.4 were made by the temperature jump technique, and comparative values of Keg were determined by a spectrophotometric titration method based on absorption difference at 550 rnp between ferriand ferrocytochrome C. Also, stopped flow experiments at 550 rnp were performed at pH 9.5. In all of these experiments, excess sodium ferrocyanide (8 X 10u3 M) wa...

The low-spin cyanide complexes of three Co(ll) carbonic anhydrases were investigated by electron paramagnetic resonance (e.p.r.) at 9 and 35GHz. Well-defined and closely axial spectra were obtained only in the absence of oxygen. Several mole equivalents of cyanidewererequired for complete formation ofthecomplexes in frozen solution, although large excesses caused abstraction of the cobalt. Expe...

I present the first clear evidence that the protein: FAD ratio in human monoamine oxidase A and bovine monoamine oxidase B has an upper limit of 65 kDa and 57 kDa per FAD, respectively. To now it had been assumed that the protein: FAD ratio was 100-120 kDa to 1 FAD and that there was one FAD per two subunits which were assumed to be of the same size. For the present work the purity of monoamine...

Results of rapid reaction experiments indicate that the first observable product formed after the reaction of oxygen with purified reduced cytochrome oxidase is a spectral form which corresponds to that of the oxidized enzyme. The latter is then slowly converted to “The Compound,” or so-called oxygenated form. These observations suggest that The Compound is not an intermediate in the cytochrome...

Tryptophanase (tryptophan: indole-lyase) from Escherichia coli has been isolated in the holoenzyme form and its absorption spectra and acid-base chemistry have been reevaluated. Apoenzyme has been prepared by dialysis against sodium phosphate and L-alanine and molar absorptivities of the coenzyme bands have been estimated by readdition of pyridoxal 5'-phosphate. The spectrophotometric titration...

The circular dichroism (CD) spectra of five myeloma and six hybridoma proteins specific for phosphocholine were measured in the 250-310-nm range. The effect on the CD spectra of adding phosphocholine was also examined. The five myeloma proteins all had distinctive native spectra and, except for M603 and W3207, unique changes occurred on ligand binding. The hybridomas were chosen as pairs from e...

Focus of this paper is the description of common used methods for hexavalent chromium measurement. This work is focused especially on commonly available spectrophotometric method based on the reaction with 1,5-diphenylcarbazide, because not every laboratory is equipped with modern devices for this pollutant measurement,. Special attention was focused on the variability possibilities of the basi...