Biological low-dose radiation effects.

It is theorized that biological responses to ionizing radiation in the low dose range are determined according to a doubly dichotomous pattern. Energy depositions fall into 2 categories: events at thermal energy levels where they may be experienced by cells as rates even at background exposure conditions, and events at energy levels of the order of 10-100 eV where damage to DNA may be caused. Variations in background exposure intensity may or may not lead preemptively to changes in the cell's capacity for response to radiation damage. High-level energy depositions lead post hoc to an initial stabilizing reaction largely leading to the fixation of the initial DNA damage, and to a subsequent restorative or palliative repair process. This model entails reinterpretation of some experimental results. The model has implications for the relationship between scientific analysis of low-dose effects and the regulatory needs for simplicity and homogeneity in risk evaluation. This represents a new challenge for the acceptability of radiation protection norms.     

The radiation hybrid database.

Since July 1995, the European Bioinformatics Institute (EBI) has maintained the Radiation Hybrid database (RHdb; http://www.ebi.ac. uk/RHdb ), a public database for radiation hybrid data. Radiation hybrid mapping is an important technique for determining high resolution maps. Recently, CORBA access has been added to RHdb. The EBI is an Outstation of the European Molecular Biology Laboratory (EMBL).     

Human genetic studies in areas of high natural radiation. VIII. Genetic load not related to radiation.

The genetic load disclosed by inbreeding has been analyzed in a multiple regression model for a population involving several localities in the state of Espírito Santo, Brazil. The inbreeding load has been estimated for number of pregnancies, abortions, stillbirths, children born alive, anomalies in general, sex ratio, infant mortality, post-infant mortality, and sterility and infertility of the couple. There was no evidence of either maternal or paternal inbreeding effects on the variables analyzed. The effect of inbreeding of the zygote was significant only for anomalies in general (B = 2.29 +/- 0.45) and infant mortality (B = 3.19 +/- 1.39). The latter result must be accepted with caution because of the many environmental causes affecting infant mortality. The B/A ratio suggested a predominantly mutational load for anomalies in general (B/A = 25), but with respect to infant mortality (B/A = 6), the ratio is regarded as an underestimate because of the environmental contribution to A and therefore not supportive of the segregational interpretation.     

Entropy of radiation in biology.

The concept of the entropy of electromagnetic radiation and the relationship between entropy and probability for radiation fields are explained. Equations for the variations of entropy and temperature in the reversible and irreversible volume changes of black radiation fields are given. Following Boltzmann and Schrödinger, it is pointed out that living matter, e.g., in a stationary state, struggles for the chance of acquiring the needed free energy by converting low-entropy solar energy radiation into high-entropy terrestrial energy radiation. The amount of energy available from a Carnot process with utilization of high-temperature (low-entropy) radiation and the influence of radiation scattering are computed. The considerations are applied to photosynthesis. Technically useful amounts of hydrogen could in principle be obtained through water photolysis by means of artificial, simulated, photosynthesis. For the purpose, the membrane principle has central importance, i.e., by means of asymmetric, vectorial, membranes separation of the primary products of photolysis is sought.     

Compound dual radiation action. I. General aspects.

The theory of dual radiation action (A. M. Kellerer and H. H. Rossi, Curr. Top. Radiat. Res. Q. 8, 85-158, 1972) has attributed the effects of ionizing radiation on eukaryotes to the production of molecular changes (sublesions) that combine pairwise to produce injury (lesions) responsible for radiation effects. If the yield of sublesions is independent of radiation quality (as is currently assumed), dual radiation action results in the well-known proportionality between the average yield of lesions and alpha D+beta D2, where beta is a radiation-independent quantity. It has, however, been observed that beta changes with radiation type. In this paper we propose an explanation of this discrepancy. Specifically, we suggest that dual radiation action-type processes where beta is variable are the result of a mechanism--termed compound dual radiation action--which consists of a sequence of simple dual radiation action processes, each process being the causative agent for the next one. The sequence, single-strand DNA breaks, double-strand DNA breaks (chromosome breaks), and exchange-type chromosomal aberrations, is one such example examined in the paper.     

Mitochondrial mutagenesis in Saccharomyces cerevisiae. I. Ultraviolet radiation.

UV efficiently induces mutations in mitDNA , conferring resistance to erythromycin. Mitochondrial chloramphenicol-resistant mutants are probably also induced by UV, but almost 90% of mutants with such phenotype are non-mitochondrial; therefore it is possible to estimate accurately the frequences of the induced presumptive mitochondrial capr mutations.