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Title: Regulation of enzyme synthesis in Euglena gracilis
Author: Javed, Q.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1988
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The expression of NADPH-specific glutamate dehydrogenase (NADPH-GDH) was examined in Euglena gracilis Klebs strain z Pringsheim in relation to light and available nitrogen source. The exposure of dark-grown resting cells to white or red light caused a transient increase in NADPH-GDH specific activity over the first 12 hours of regreening. Nitrogen-starved or cells grown on glutamate had high NADPH-GDH activity but activity was completely repressed in cells grown on ammonium bicarbonate as sole nitrogen source. These characteristics of the dehydrogenase suggest that the enzyme has a catabolic function in Euglena generating NH+4 from glutamate under conditions of nitrogen limitation. NADPH-GDH was purified from glutamate-grown cells. The homogenously pure protein was characterised (subunit relative molecular mass, 45,000 daltons) and used for antibody production in rabbit. Monospecific anti-(NADPH-GDH) serum obtained was used to detect nascent NADPH-GDH in rabbit reticulocyte lysates programmed with Euglena poly(A)+RNA in order to determine the relative abundance of NADPH-GDH poly(A)+RNA in relation to enzyme expression. By immunochemical titration using the specific antiserum the increase in NADPH-GDH activity in glutamate-grown and regreening cells was shown to be the result of an increase in enzyme protein. Poly(A)+RNA extracted from cells grown on different nitrogen sources and regreening cultures was used to programme reticulocyte lysates. The immunoprecipitation of nascent NADPH-GDH from lysates showed that changes in enzyme levels in response to substrate provision or during regreening were not reflected in levels of its poly(A)+RNA. The results suggest that the synthesis of NADPH-GDH is regulated primarily at the post-transcriptional level in Euglena. NADPH-GDH poly(A)+RNA could not be detected on polysomes of dark-grown resting cells although the abundance of poly(A)+RNA encoding NADPH-GDH was apparently unaltered in these cells. NADPH-GDH was detected on polysomes from dark-grown resting cells after 6 and 12 hours of illumination. This implies that light elicits a mobilisation of a pre-existing NADPH-GDH poly(A)+RNA onto polysomes of regreening cultures promoting enzyme synthesis.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available