Descripción: Solvation of excess electrons in supercritical ammonia along the T = 450 K isotherm was investigated. Equilibrium aspects of solvation were analyzed using combined path integral-molecular dynamics techniques. Observations showed transition from localized to quasifree states at approximately one fourth of the triple point density.

Descripción: General constraints for invariance of magnetic properties in a gauge transformation are analyzed. Sum rules relative to the transformation from Coulomb to Landau gauges are examined in particular. Numerical tests for hydrogen fluoride, water, ammonia, and methane molecule have been carried out in large basis set calculations, using random-phase approximation. The conditions for invariance are severe conditions for accuracy of variational molecular wave functions. © 1995 American Institute of Physics.

Descripción: 1. 1. Gel filtration on Sephadex G-100 and Sepharose 4B were used to redetermine the molecular weight (MW) of porphobilinogenase, deaminase and isomerase purified from different sources, and determine the MW of these enzymes purified from Eugtena gracilis. 2. 2. Results reported here, indicate that porphobilinogenase can be found, into three different molecular forms, tetramers, dimers and monomers according to the source organism. 3. 3. It is proposed that minimal functional structure of PBGase is a hybrid protomer of MW 25,000, composed by two different domains, in a ratio of 1 mol of deaminase, MW 20,000 to 1 mol of isomerase. MW 5000. 4. 4. A model explaining the occurrence of different MW species of PBGase in nature and the possible interconversion among the various forms is postulated. © 1980.

Descripción: 1. 1. Preliminary experiments with Euglena gracilis indicated that an endogenous factor which modified enzymic synthesis of porphyrinogens from PBG, was present in Homogenates (H) and Supernatant (S) fractions. 2. 2. When H or S was stored at 4-6°C, enzymic activity underwent an apparent spontaneous activation, increasing by as much as 7.5-8 times after 14 and 22 days of aging respectively. 3. 3. Experiments were carried out to detect, isolate and identify this factor. S and H were heated and the effect of the protein free supernatants (Hø,Sø) on activity were tested. By gel filtration of H and S, a low molecular weight compound (FH, FS) was separated, and the activity of the eluated protein (PrH, PrS) was enhanced 10-12 times. 4. 4. Addition of either Hø, Sø, FH or FS to different E. gracilis preparations increased their activities, suggesting the existence of a low molecular weight, heat-stable factor which would act stimulating enzymic synthesis of porphyrinogens. However some differences in the properties of the factor present in Hø or Sø and that present in FH or FS were observed. 5. 5. Studies on the FH and FS, confirmed that the factor was heat-stable, upon storage at 4°C its activation properties were not modified; but they were destroyed by basic or acid treatment. 6. 6. The same degree of activation as that produced by FH and FS on H, S, PrH and PrS, was obtained by replacing the factor solution by 10-7M folic acid or 10-3-10-2M Gluthation (GSH); however, neither the factor nor folic acid or GSH has any effect on the pellet enzyme, either bound to the membrane or solubilized by means of a chaothropic agent. 7. 7. The potential use of this factor in the treatment of acute porphyrias was indirectly investigated, by treating acute intermittent porphyria patients in early or acute attack with folic acid; after its oral administration at a dose of 30 mg daily for not longer than 10 days, both biochemical and clinical recovery followed. 8. 8. A scheme to explain the role of this factor in acting and controlling porphobilinogenase activity in E. gracilis is proposed. © 1981.

Descripción: 1. 1. Studies on porphyrin biosynthesis from exogenus ALA, at various time intervals as well as direct enzyme measurements (aminolevulimc acid dehydratase (ALA-D); porphobilinogenase (PBG ase) and deaminase were carried out in hemolysates of human erythrocytes from healthy controls and patients with lead poisoning (Pb), acute intermittent porphyria (AIP), porphyria cutanea tarda (PCT), erythropoietic protoporphyria (EPP), variegate porphyria (VP) and congenital erythropoietic porphyria (CEP). 2. 2. Inhibited ALA-D in Pb, reduced PBGase and deaminase in AIP, lower uroporphyrinogen decarboxylase in PCT, and diminished isomerase in CEP, were confirmed. In addition, ALA-D was found, reduced in AIP, unchanged in PCT and increased in EPP, VP and CEP. PBGase and deaminase were, on the other hand, increased in Pb and PCT, unchanged in VP and diminished in EPP and CEP. 3. 3. Total porphyrin biosynthesis is a function of time; compared to normals, is lower in CEP and AIP, but higher in PCT. 4. 4. The porphyrin profile changes along the time; uroporphyrin increases at longer intervals while that of coproporphyrin concomitantly diminished. A significance enhancement of octacarboxylic porphyrins was observed during the entire duration of the incubation in PCT hemolysates. In CEP the main porphyrin was always uroporphyrin I. 5. 5. Studies on both total porphyrins formed and their distribution were performed in hemolysates from cases of non-hereditary and hereditary PCT and AIP, before and after therapy. © 1980.

Descripción: Vertical excitation and electron detachment energies associated with the optical absorption of iodide ions dissolved in supercritical ammonia at 420 K have been calculated in two limiting scenarios: as a solvated free I- ion and forming a K+ I- contact ion pair (CIP). The evolution of the transition energies as a result of the gradual building up of the solvation structure was studied for each absorbing species as the solvent's density increased, i.e., changing the N H3 supercritical thermodynamic state. In both cases, if the solvent density is sufficiently high, photon absorption produces a spatially extended electron charge beyond the volume occupied by the solvated solute core; this excited state resembles a typical charge-transfer-to-solvent (CTTS) state. A combination of classical molecular dynamics simulations followed by quantum mechanical calculations for the ground, first-excited, and electron-detached electronic states have been carried out for the system consisting of one donor species (free I- ion or K+ I- CIP) surrounded by ammonia molecules. Vertical excitation and electron detachment energies were obtained by averaging 100 randomly chosen microconfigurations along the molecular dynamics trajectory computed for each thermodynamic condition (fluid density). Short- and long-range contributions of the solvent-donor interaction upon the CTTS states of I- and K+ I- were identified by performing additional electronic structure calculations where only the solvent interaction due to the first neighbor molecules was taken into account. These computations, together with previous experimental evidence that we collected for the system, have been used to analyze the solvent effects on the CTTS transition. In this paper we have established the following: (i) the CTTS electron of free I- ion or K+ I- CIP presents similar features, and it gradually localizes in close proximity of the iodine parent atom when the ammonia density is increased; (ii) for the free I- ion, the short-range solvent interaction contributes to the stabilization of the ground state more than it does for the CTTS excited state, which is evidenced experimentally as a blueshift in the maximum absorption of the CTTS transition when the density is increased; (iii) this effect is less noticeable for the K+ I- ion pair, because in this case a tight solvation structure, formed by four N H3 molecules wedged between the ions, appears at very low density and is very little affected by changes in the density; (iv) the long-range contribution to the solvent stabilization can be neglected for the K+ I- CIP, since the main features of its electronic transition can be explained on the basis of the vicinity of the cation; (v) however, the long-range solvent field contribution is essential for the free I- ion to become an efficient CTTS donor upon photoexcitation, and this establishes a difference in the CTTS behavior of I- in bulk and in clusters. © 2007 American Institute of Physics.

Descripción: 1. 1. A method for the isolation and purification of porphobilinogenase, porphobilinogen deaminase and uroporphyrinogen isomerase from avian erythrocytes is described. 2. 2. Some properties of the isolated enzymes were studied. The optimal pH for porphobilinogenase and deaminase was 7.4. Purified porphobilinogenase was resolved into three bands on starch gel electrophoresis. The molecular weight of the purified enzymes was determined by gel filtration. The presence of porphobilinogen or NH4 + at certain concentrations afforded protection against heat inactivation of isomerase, the heat labile enzyme. Initial porphyrin formation by porphobilinogenase was linear with time. 3. 3. The action of various compounds added to the system was studied. Thiol reagents inhibited both porphobilinogenase and deaminase, indicating the presence of thiol groups essential for activity. NH4 +, hydroxylamine, adenine, ADP, ATP, some dicarboxylic acids and 2-methoxy-5-nitrotropone inhibited deaminase. © 1971.

Descripción: 1. 1. This paper confirms the increase in sensitivity obtained for erythrocyte UIS measurement by pre-incubation of the red cells in a 0.2% Triton-X 100 solution containing 1 mmol/1 ZnSO4 and dithiothreitol as described by Piepkorn et al. (1978). 2. 2. To achieve optimal precision in this assay a substrate concentration of delta aminolaevulinic acid (ALA) of 1000nmol/ml is required. Interpretation of the results obtained by this method is discussed and its use in the detection of both latent and acute intermittent porphyria is demonstrated. Comparative studies were carried out by using the Batlle et al. (1978) method and a modification employing ALA as substrate. © 1980.

Descripción: 1. 1. Porphyrin biosynthesis from 5-aminoevulinic acid (ALA) was investigated using the technique of tissue explant cultures, in both human breast cancer and its original normal tissue. 2. 2. The activity of ALA-dehydratase, porphobilinogenase and uroporphyrinogen decarboxylase was directly determined in both tumor and normal mammary tissues. 3. 3. Porphyrin synthesis capacity of human breast carcinoma was 20-fold enhanced, as compared with normal tissue, at least between the stages of porphobilinogen and coproporphyrinogen formation. 4. 4. The activity of the three enzymes examined was always lower in normal tissue than in tumoral tissue. 5. 5. Present findings show that porphyrin biosynthesis is increased in breast cancer tissue. © 1990.