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J J Mitchell

Publications and source records attributed to J J Mitchell.

45 records · Page 3Linked to original sources
PubMed1980

The effect of alcohols on guanosine 5'-diphosphate-3'-diphosphate metabolism in stringent and relaxed Escherichia coli.

The effects of a series of alcohols on the stringent response system of Escherichia coli were studied. The alcohols used could be divided into two groups on the basis of the response of pppGpp and ppGpp to the growth downshift induced by the alcohols. The cells responded to the alcohols, methanol, ethanol, and propanol, as if they were being starved of amino acids. In the stringent strain CP78 these alcohols induced pppGpp and ppGpp accumulation and curtailed RNA synthesis, whereas in the relaxed strain CP79, both of these responses were absent. It was determined that this response was most likely due to an interference by these alcohols with the uptake of amino acids required by these strains. By contrast both stringent and relaxed cells elevated their level of ppGpp and decreased RNA accumulation when treated with butanol or pentanol. This response is similar to the effect of carbon source limitation. It was determined that the elevation of ppGpp in the stringent strain was primarily the result of increased ppGpp synthesis in response to these alcohols. In the relaxed strain the rise in ppGpp was dependent on a decrease in ppGpp degradation coupled with a moderate increase in ppGpp synthesis. This stimulation of ppGpp synthesis in relaxed cells, although small, suggests the existence of an enzyme distinct from stringent factor which is capable of synthesizing ppGpp. Data are presented which suggest that the activity of this enzyme is coupled to the potential for protein synthesis and energy availability of the cell, perhaps being regulated by the overall ratio of unchanged to amino-acylated tRNA.

Alcohols↗
PubMedDate not supplied

Age-related changes in [3H]MK-801 binding in the Fischer 344 rat brain.

In this study we tested the hypothesis that the efficacy of L-glutamate to stimulate [3H]MK-801 binding to the NMDA receptor/channel complex is altered as a function of aging. L-Glutamate, or related excitatory amino acid (EAA), is the endogenous neurotransmitter of the NMDA receptor/channel complex. These studies examined the efficacy and potency with which L-glutamate produces receptor activation, channel opening and subsequent MK-801 binding as a function of increasing age by comparing dose-response curves (EC50 and Emax) from 6-, 12-, and 24-month-old F-344 rats. The number of NMDA receptors, as determined by [3H]MK-801 binding in the presence of a saturating concentration of L-glutamate, was reduced in the inner frontal cortex, entorhinal cortex and the lateral striatum in aged rats when compared with young adults. When a range of L-glutamate concentrations were used, differences in Emax were noted in the same brain regions in addition to several others in aged and middle-aged animals when compared with young-adult animals. No changes in EC50 values were noted in any of the brain regions at either age when compared with young-adults.

Aging↗