PubMed Health⌕ Search

Biomedical subjects

C A Potter

Publications and source records attributed to C A Potter.

4 recordsLinked to original sources

A simple method for assessing exposure to internal emitters.

One of the most challenging aspects of regulatory compliance can be demonstrating compliance with internal dosimetry requirements. For long-lived alpha-emitting radionuclides in particular, the sensitivity and accuracy of bioassay analysis and whole body counting may not allow for adequate assessment of intakes. Simple and effective measures can be used to control the workplace for the internal hazards associated with long-lived radioactive material using methods that measure directly the air to which workers are exposed. This paper provides an easy assessment tool that uses direct measurement of the specific activity of dusts in breathing zone air to evaluate internal exposures. Using this method, sensitive assessments can be made to determine if intakes are likely to have occurred and, if so, at what magnitude. It is not a substitute for confirmatory bioassay or whole body counting but a simple method to evaluate expectations for internal exposures.

Air Pollution, Radioactive↗

A defense in depth approach to radiation protection for 125I production activities.

Not all operational radiation protection situations lend themselves to simple solutions. Often a Radiation Protection Program must be developed and implemented for difficult situations. A defense in depth approach to radiation protection was developed for 125I production activities. Defense in depth relies on key radiation protection elements that tend to be mutually supportive and in combination provide reasonable assurance that the overall desired level of protection has been provided. For difficult situations, defense in depth can provide both a reasonable and appropriate approach to radiation protection.

Humans↗

End-product control of enzymes of branched-chain amino acid biosynthesis in Streptomyces coelicolor.

In streptomycetes, the branched-chain amino acids leucine, isoleucine and valine may serve as precursors for commercially important polyketides, and it is of interest to investigate whether the availability of these amino acids affects the production of the secondary metabolites derived from them. This paper reports studies on end-product control in the model organism Streptomyces coelicolor of the enzymes acetohydroxy acid synthase (AHAS) and isopropylmalate synthase (IPMS), mediating steps in the pathways to isoleucine-valine and leucine respectively. Specific activities of both enzymes were similarly affected when minimal medium was supplemented with the amino acids singly or in combination. Isoleucine alone caused a 2- to 3-fold increase, while all three amino acids caused a 5- to 8-fold decrease. Growth of an ilv auxotroph in media with limiting isoleucine gave enzyme specific activities 4- to 6-fold higher than in unsupplemented minimal medium. Spontaneous mutants were obtained by growing S. coelicolor on minimal medium containing 4-azaleucine. At lease four patterns of end-product control were found among the mutants, one of which showed high constitutive levels of both enzymes (7- and 15-fold above unsupplemented minimal medium values for AHAS and IPMS respectively). It is concluded that the variation in specific activities of the two enzymes under different physiological and genetic conditions spans a range of around 50 to 100, and that S. coelicolor has molecular mechanisms capable of producing this response.

2-Isopropylmalate Synthase↗