Biomedical subjects

G K York

Publications and source records attributed to G K York.

22 records · Page 2Linked to original sources

PubMed1966

Effect of pimaricin on the resistance of Saccharomyces cerevisiae to heat, freezing, and ultraviolet irradiation.

Exposure of washed cells of Saccharomyces cerevisiae C-299 to inhibitory concentrations of pimaricin decreased resistance to lethal temperatures and to freezing and thawing. Varying the pH of the recovery medium had little effect on the decrease in heat resistance, but addition of peptone or yeast extract resulted in a partial recovery of apparent heat resistance. Addition of peptone or calcium ion to the heating menstruum did not affect the reduction in resistance caused by pimaricin. Varying the composition of the recovery medium similarly affected the resistance to freezing the thawing of pimaricin-exposed and unexposed cells. Sensitivity to ultraviolet light was apparently not affected by pimaricin either by preliminary exposure or when irradiated in the presence of pimaricin. It is suggested that pimaricin lowers the heat resistance of S. cerevisiae by depleting essential nutrients of the cells through a disruption of permeability, and that heat-damaged cells cannot resynthesize these nutrients. It is also suggested that spoilage of acid foods by S. cerevisiae may be retarded by a combination of mild heat treatment and the addition of pimaricin.

Antifungal Agents↗

PubMed1965

Effect of several environmental conditions on the "thermal death rate" of endospores of aerobic, thermophilic bacteria.

The composition of the recovery medium affected the apparent heat resistance of Bacillus stearothermophilus when the pH of the medium was 7.0 but not when the pH was 6.5. The rate of thermal death at 110 C was exponential. Deviations from exponential rates of thermal death during the initial phases of heating at 96 C were observed with endospores of B. coagulans under different conditions of sporulation. Additionally, the apparent heat resistance was influenced by the composition of the media used for sporulation and recovery and by the composition of the suspending menstruum. The presence of 0.001 m sorbic acid in the suspending menstruum at pH 7.0 and the temperature of incubation of the cultures after heating did not affect the apparent heat resistance of B. coagulans. Several explanations are discussed for the observed deviations from exponential thermal death rates and the effect of the environment on the apparent heat resistance of B. coagulans.

Bacillus↗

PubMedDate not supplied

Stimulation by cigarette smoke of glutathione peroxidase system enzyme activities in rat lung.

This study was undertaken to evaluate the effect of in vivo cigarette smoke exposure on glutathione peroxidase--related enzyme systems of the rat lung. These enzymes, acting in concert, are thought to be responsible for disposing of toxic lipid peroxides in pulmonary tissue. Thirty-day-old rats were exposed to thirteen cigarettes per day for 21 days with a Walton reverse-smoking exposure apparatus. After 21 days of smoke exposure, the activities of glutathione peroxidase, glutathione reductase, and glucose-6-phosphate dehydrogenase were increased 34%, 24%, and 38%, respectively, over control values. This level of cigarette smoke exposure did not cause detectable histological lesions. We present the hypothesis that short-term, low-level cigarette smoke exposure is capable of initiating metabolic alterations in lung cells at exposures at which histological changes are not detectable by light microscopy.

Animals↗

PubMedDate not supplied

Biochemical effect of ozone exposure in rats exposed to cigarette smoke.

Rats were exposed to three cigarettes per day for 35 days, under realistic conditions. Pulmonary glucose-6-phosphate dehydrogenase (G-6-PD) activity in the exposed animals increased 27% over control values (P less than .05). Subsequent exposure to acute, high-dose ozone (3 ppm for 4 hr) decreased the augmented G-6-PD activities to near normal levels, whereas ozone exposures in animals not exposed to cigarette smoke caused mild decreases in pulmonary G-6-PD activities. The importance of these findings with respect to the susceptibility of the smoker to oxidant exposures is unknown.

Animals↗