Biochemical properties of esterase 6 in Drosophila melanogaster were investigated using partially purified preparations from three genotypes, 1/1, 1/2, and 2/2. The molecular weight of the enzyme is estimated to be about 90,000, and treatment with sodium dodecylsulfate cleaves the enzyme into four units with a molecular weight of about 22,000. The activity toward 28 naturally occurring esters was assayed and shown to vary considerably with substrate, the 1/1 preparation having in general higher activity than 1/2 and 2/2, which were very similar. Heat sensitivity, the effect of metal ions, and the effects of the presence or absence of an end product were also studied. The differences demonstrated between allozymes would allow considerable scope, under appropriate conditions, for differential selection to operate between genotypes.
Chromosome aberration analysis has been the basis of one of core tests in genetic toxicology since guidelines were first established (DHSS (1981) Guidelines for the Testing of Chemicals for Mutagenicity. Prepared by the Committee on Mutagenicity of Chemcials in Food, Consumer Products, and the Environment, Department of Health and Social Security. Report on Health and Social Subjects, No. 24. Her Majesty's Stationery Office, London; IPCS (1985) Guide to short-term tests for detecting mutagenic and carcinogenic chemicals prepared for the IPCS by the International Commission for Protection against Environmental Mutagens and Carcinogens. Geneva, WHO). The technique consists of microscope examination of preparations of chromosomes, usually mammalian, for clastogenicity (chromosome breakage events), and agents which induce such changes are considered genotoxic.There are a number of different types of aberrations, and within types, considerable variation in their appearance. This chapter addresses aberration classification, their appearance, frequency and fate, and the range within aberration types, potential mis-classifications, and data recording and interpretation.
The frequency of dicentrics + ring (dic/cell) and total chromosome aberrations (dicentrics, rings and excess acentrics, etc.) per cell (TAb/cell) has been studied in 50 male and female volunteers after high or low dose rate (HDR, LDR) irradiation of peripheral blood lymphocytes. The mean male aberration frequencies per cell after HDR irradiation were 0.38 dic/cell and 0.61 TAb/cell; following LDR irradiation, the mean aberration frequencies were 0.28 dic/cell and 0.45 TAb/cell. Equivalent female values after HDR irradiation were 0.42 dic/cell and 0.71 TAb/cell; after LDR irradiation, the mean aberration frequencies were 0.30 dic/cell and 0.48 TAb/cell. Analysis of variance showed that there was a highly significant difference between males and females have a greater HDR, but not LDR, irradiation It is concluded from this study that females have a greater variability in their radioresponse, and that this variability is related to progesterone, which has a profound effect upon radiosensitivity, as measured by cytogenetic end points.
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