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Biomedical subjects

M S Murthy

Publications and source records attributed to M S Murthy.

At least 91 records · Page 5Linked to original sources
PubMed1978

Determination of radiation equivalence of the chemical furylfuramide (AF-2) for the induction of gene conversion in diploid yeast and estimation of genetic risk to the Japanese population.

Dose--effect relationships for the induction of gene conversion by AF-2 in diploid yeast have been established. On the basis of these, the rec value for AF-2 for induction of gene conversion has been calculated to be 0.085 microgram/ml.h. This compares well with the rec values obtained with other test systems and other genetic end-points. The genetic burden to the Japanese population due to consumption of AF-2 is estimated to be equivalent to 55 millirec. However, uncertainties in the consumption of AF-2 per person and its metabolic detoxication tend to lower this value to, probably, a small fraction of that due to natural background ionizing radiation.

Alleles↗
PubMed1978

Determination of radiation equivalence of ethyl methanesulphonate (EMS) for induction of gene conversion in diploid yeast.

A unit Rad-Equivalent Chemical (REC) has been suggested for purposes of quantitating the mutagenic hazards of chemicals. The usefulness of this approach is demonstrated by the establishment of a constant relationship between the forward mutation frequency and haploid genome size in various organisms for both radiation and chemical EMS. However, it is necessary to determine the radiation equivalence of chemicals in as many organisms and for as many end-points as possible. For end-points we are limited to forward mutations. Another relevant genetic end-point of interest in this regard is gene conversion which can also monitor any kind of DNA damage in a suitable diploid system. Hence, we have determined the REC value for EMS in diploid yeast with gene conversion as the end-point. This agrees well with the REC values estimated in a number of organisms with forward mutation as the end-point. This finding further underlines the generality of the REC concept.

Alleles↗
PubMed1978

On the nature of damage involved in liquid-holding recovery in diploid yeast after gamma- and alpha-irradiation.

Cells surviving after liquid-holding recovery following gamma- and alpha-irradiations are found to be slightly more sensitive to a second series of radiation doses. Further, the shoulder on the gamma survival curve of the pre-irradiated and liquid-held cells disappears. The shoulder and sensitivity are restored only when these cells are grown in broth before the second series of doses. In addition to this, liquid-holding recovery reduces progressively if the cells after irradiation are incubated in broth for different periods of time before holding. These observations suggest that: (1) the so-called potentially lethal damage may consitute that part of the sub-lethal damage which interact with one another to form lethal damage; (2) during liquid-holding, the interaction among sub-lethal damage transforming them to the status of lethal damage is inhibited; (3) the 'recovered' cells are saturated with sub-lethal damage, the repair of which will be completed only when the cells are placed in a nutrient medium. The inhibitory process is not a passive one, but requires energy metabolism.

Alpha Particles↗
PubMed1976

Liquid holding recovery in stationary and log phase cultures of diploid yeast exposed to gamma and alpha radiations.

The kinetics of liquid-holding recovery (LHR) in diploid yeast after gamma and alpha irradiation is studied. In case of stationary phase culture the rate and extent of LHR is found to be greater for gamma-ray-induced damage than for alpha-ray-induced damage. At 10% survival level, the half-time for recovery is 5.2 h for gamma-ray damage and 12 h for alpha-ray damage. Further, while the recovery factor for alpha damage reaches saturation at 5% survival level, that for gamma damage continues to increase as survival level decreases. Oxygen is required for the recovery process during LH after gamma irradiation. The cells can recover to the same extent from both oxygen-dependent and oxygen-independent components of damage. Log phase cells containing a high per cent of budding cells, however, exhibit negative liquid holding effect after gamma irradiation.

Alpha Particles↗
PubMed1976

Dependence of the expression of the radiation-induced gene conversion to arginine independence in diploid yeast on the amino acid concentration: effect on allelic mapping.

The yield of radiation-induced gene conversion to arginine independence in diploid yeast depended on the concentration of the amino acid both in the plating medium and in the intracellular pool. By depletion of the level of arginine in the intracellular pool of amino acid or by provision of arginine at 0.4 mg/l of the plating medium the yield was varied by a factor as high as 20. This may be important in studies of the genetic mapping of alleles based on the slope of conversion frequency versus dose line.

Amino Acids↗
PubMed1976

Primary intimal sarcoma of pulmonary valve and trunk with osteogenic sarcomatous elements. Report of a case considered to be pulmonary embolus.

A 49-year-old woman had a six-week history of increasing shortness of breath and fatigue. X-ray films and pulmonary scans showed multiple areas of emboli, especially in the right lung. Treatment with heparin was unsuccessful, and although a repeat scan showed only slight changes, the patient's condition deteriorated. Acute pulmonary edema and ventricular tachycardia preceded her death. Autopsy revealed a primary intimal sarcoma with osteogenic elements arising in the posterior leaflet of the pulmonary valve and obstructing the main pulmonary artery and its right branch.

Female↗
PubMed1975

Non-equivalence of YEPD and synthetic complete media in yeast reversion studies.

In yeast reversion studies, assay of the total number of cells is made by plating irradiated cells on agar plates containing yeast extract, peptone and dextrose (YEPD) medium. The number of revertants are scored by plating cells on synthetic complete (SC) medium deficient in the particular nutrient for which the reversion is tested. In this procedure equivalence for cell survival between the YEPD and the SC media is always assumed. However it is shown in this paper that this assumption is valid only up to dose levels where cell killing is not significant. At high doses, survivals on the two media differ significantly from each other for both high and low LET radiations. This difference influences the slope of the reversion frequency curve at high doses. Since the reversion frequency is expressed with reference to the number of survivors after a given radiation dose, it is essential to see that the same chance of survival is offered to the reverted and unreverted cells. Even though reversion is reported to vary linearly with dose, it is found that this linearity is restricted only to dose levels where cell killing is not significant. At higher doses, the reversion frequency varies in a very complex manner with dose for both high and low LET radiations. The complexity depends further on the reference medium chosen.

Alpha Particles↗
PubMed1975

Post-irradiation modifications of radiation-induced heteroallelic reversion in diploid yeast: effect of nutrient broth.

The effect of post-irradiation growth in complete rich medium on the expression of the reversion to arginine-independence induced by gamma and alpha radiation in a heteroallelic diploid yeast strain (Saccharomyces cerevisiae BZ34) has been studied. During the post-irradiation treatment the reversion frequency increased, reached a peak at about 90 min and decreased thereafter reaching a constant value for treatment periods exceeding 6 h. As determined by the increase in number of budding cells, extensive DNA synthesis took place in cells incubated only in the nutrient medium and not in the omission medium. Hence the observed increase in the reversion frequency is explained on the basis that post-irradiation DNA synthesis is necessary for the expression of gene conversion. The decrease in the reversion frequency for continued treatment with yeast extract, peptone, dextrose (YEPD) is related to the fact that only one daughter of the post-irradiation first cell division is a revertant. The broth effect was not lost when the irradiated cells were first incubated for 90 min in arginine-less medium and then transferred to the broth. Similarly, the broth effect persisted even at doses high enough to induce considerable division delay. These results suggest that the radiation-induced pre-conversional lesions are not susceptible to repair by alternative pathways.

Alleles↗