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R Itoh

Publications and source records attributed to R Itoh.

209 records · Page 12Linked to original sources
PubMed1976

Pigeon liver amidophosphoribosyltransferase. Ligand-induced alterations in molecular and kinetic properties.

Amidophosphoribosyltransferase (EC 2.4.2.14) has been partially purified from pigeon liver, and ligand-induced alterations in molecular and kinetic properties have been studied. In Tris-HCl buffer the predominant form of the enzyme has an s20,w of 5.9 +/- 0.7, Stokes radium of 42 A, and estimated molecular weight of 102,000. Incubation with phosphoribosylpyrophosphate (PP-ribose-P) results in an increase in the s20,w to 7.9 +/- 0.6, Stokes radius to 53 A, and estimated molecular weight to 172,000. Incubation of this larger form with purine ribonucleotides leads to a decrease in the molecular weight of amidophosphoribosyltransferase that is proportional to the concentration of purine ribonucleotide. Purine ribonucleotides produce sigmoidal kinetics with respect to the substrate PP-ribose-P, with Hill coefficients of 1.4 to 1.6 and 1.8 to 2.0 in the presence of AMP and GMP, respectively. Incubation with 0.6 M KCl leads to sigmoidal kinetics. Hill coefficient of 1.8 and dissociation of the larger form of amidophosphoribosyltransferase. Inorganic phosphate has complex effects upon the enzyme. In 25 mM potassium phosphate buffer the enzyme aggregates to a large form with an s20,w of 8.3 +/- 0.2, Stokes radius of 53 A, and estimated molecular weight of 181,000. Inorganic phosphate and PP-ribose-P both stabilize the enzyme to storage in vitro at 4 degrees. However, inorganic phosphate is 4 times more effective than PP-ribose-P in preventing inactivation of the enzyme by sodium dodecyl sulfate. Inorganic phosphate produces sigmoidal kinetics with respect to PP-ribose-P, Hill coefficient of 1.5. The interaction coefficients for AMP and GMP are reduced from 1.8 to 1.2 and 2.2 to 1.4, respectively, in the presence of 25 mM potassium phosphate. It is concluded that pigeon liver amidophosphoribosyltransferase is a complex allosteric protein whose activity is regulated by a series of conformational changes induced by a number of ligands.

Adenosine Monophosphate↗
PubMedDate not supplied

The use of perfluorocarbon liquids in diabetic vitrectomy.

Three eyes of 3 patients were operated on for severe proliferative diabetic retinopathy with tractional and/or rhegmatogenous retinal detachment using perfluoro-n-octane as temporary tamponade. The perfluorocarbon was removed at the end of the procedure. Intraocular tamponade was provided by a long-acting gas in all eyes. The intraoperative use of perfluorocarbon effectively facilitated retinal flattening and endophotocoagulation. Anatomical success was obtained in all 3 cases, with a minimum follow-up of 10 months. Visual acuity improved in all eyes. The main advantages of perfluorocarbon are that it enables easy flattening of the posterior retinal folds and effective endophotocoagulation with good visual conditions.

Diabetic Retinopathy↗
PubMedDate not supplied

Contrast-enhanced MR angiography: the effects of k-space truncation on luminal representation in a carotid artery phantom model.

Using carotid bifurcation phantom models with different degrees of stenoses, we evaluated the accuracy of vessel lumen representation on MR images obtained from the inverse Fourier transform of different k-space percentages. Our results show that the lower thresholds of truncated k-space sampling are dictated by the severity of luminal narrowing. The defined thresholds may help improve efficiency of 3D MR imaging of the carotid arteries while maintaining adequate luminal representation.

Carotid Arteries↗
PubMedDate not supplied

Diffusion tensor MR imaging of the brain: effect of diffusion weighting on trace and anisotropy measurements.

BACKGROUND AND PURPOSE: In human brain, the relationship between MR signal and b value is complicated by cerebral perfusion, restricted diffusion, anisotropy, cellular membrane permeability, and active cellular transport of water molecules. Our purpose was to evaluate the effect of the number and strength of diffusion-sensitizing gradients on measured isotropic apparent diffusion coefficients (ADCi), fractional anisotropy (FA), and their respective SD in different anatomic locations of the brain. METHODS: Quantitative apparent diffusion coefficients and diffusion anisotropy brain maps were obtained from 10 healthy volunteers by using six different levels of diffusion weighting (b0 = 0, bl = 160, b2 = 320, b3 = 480, b4 = 640, and b5 = 800 s/mm2), applied sequentially in six different directions (Gxx, Gyy, Gzz, Gxy, Gxz, Gyz) and coupled to a single-shot spin-echo echo-planar (2,045/115 [TR/TE]) MR imaging technique. ADCi, FA, eigenvalues (lambda1, lambda2, lamdba3)1 of the principal eigenvectors, and their respective SD were measured from seven different anatomic locations in the brain. Repeated measures analysis of variance was used to evaluate for the existence of significant differences in the average and SD of the calculated ADCi and FA as a function of the number and strength of b values. When a difference existed, the Bonferroni t method was used for paired comparisons of the groups. RESULTS: The measured ADCi was affected by the number and strength of b values (P < .05). The SD of the ADCi was affected by the strength (P < .05) but not the number of b values (P > .05). The measured FA was unaffected by the number and strength of b values (P > .05). The SD was affected by the number and strength of b values (P < .05). CONCLUSION: The number and strength of b values do influence measures of diffusion and anisotropy. Attention to the choice of diffusion sensitization parameters is important in decisions regarding clinical feasibility (acquisition time) and normative measures.

Adult↗