Inhibition by saccharin of glucose-6-phosphatase: effects of alloxan in vivo and deoxycholate in vitro.

Inhibition by saccharin of rat liver glucose-6-phosphatase (EC 3.1.3.9) generally decreased as the pH increased in the range pH 4-8. This pattern was exhibited by homogenates from control and alloxan-treated animals assayed each in the absence and presence of 0.2% (w/v) deoxycholate. Saccharin inhibited in competitive fashion with respect to glucose-6-phosphate (glucose-6-P). There was a small increase in Km (glucose-6-P) but not K1 (saccharin) values in alloxan-treated rats when assays were conducted in the absence of deoxycholate. In the presence of this detergent there was no significant difference in these kinetic parameters between the alloxan-treated and control groups. Deoxycholate decreased Km (glucose-6-P) and increased K1 (saccharin) values. Calculations using these kinetic parameters indicate that, under usual hepatic glucose-6-P concentrations and relatively high levels of saccharin in liver, the inhibition by saccharin of glucose-6-phosphatase is unlikely to be of major significance in vivo.     

Measurement of endogenous alloxan in human blood

For determination of endogenous alloxan content in blood of healthy donors it was stabilized by rapid lowering pH in a sample to 2.0. Alloxan was then allowed to form a colored product in a reaction with [ital]o-phenylenediamine and its content was measured by spectrophotometry using an internal calibration curve. Analysis of 75 blood samples of healthy volunteers has shown that in most donors alloxan concentrations vary from 41 to 265 μmol/l. However, in a small group of healthy people alloxan levels greatly exceeded the above-mentioned limit.     

Deoxyribonuclease activity in the tissues of X-ray irradiated animals with alloxan diabetes

Fractionated X-irradiation (a cumulative dose of 12.9 mC/kg) of animals with alloxan diabetes caused different, with respect to direction and degree, changes in liver nuclease system than those observed in intact animals after similar irradiation. This indicates that insulin is involved in a metabolic response of the organism to irradiation with relatively small doses.     

In vivo and in vitro dielectric properties of animal tissues at radio frequencies

An open-ended coaxial line and an improved measurement method employing a computer controlled network analyzer were used to measure the permittivity of cat tissues. Muscle, spleen, kidney cortex, liver,and brain cortex were measured in vivo and in vitro at frequencies between 100 MHz and 8 GHz. The differences between the permittivities of these cat tissues, in the aforementioned range of frequencies, when measured in vivo and a few (up to four) hours after death, were found to be within the experimental uncertainty.     

Phosphorylation of aminoacyl-tRNA synthetase preparations of rat liver tissues in vivo and in vitro

The capacity for phosphorylation was studied in aminoacyl-tRNA synthetases isolated from the rat liver after introducing Na2H32PO4 to the organism as well as in the in vitro experiments. Some kinetic characteristics of this reaction were investigated. The velocity of the aminoacyl-tRNA synthetases phosphorylation reaches its maximum 5 minutes later, and the enzyme saturation with substrate occurs at low concentration of the latter. The values of Km, Vmax and V0 are 1.27 x 10(-2) mg/ml, 8.33 mumol 32P/mg per 1 min and 6.09 mumol 32P/mg per 1 min, respectively. A conclusion is drawn that in the in vivo and in vitro experiments there occurs phosphorylation of the total preparation of aminoacyl-tRNA synthetases and individual lysyl-tRNA synthetase.