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Title: The catabolic aspect of nitrogenase turnover in a model cyanobacterial system
Author: Reade, J. P. H.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1995
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When grown under 12hr. diurnal illumination Gloeothece cultures show N2 fixation to be confined to the period of darkness. Immunochemical study demonstrated that both proteins of the nitrogenase complex (dinitrogenase and dinitrogenase reductase) appeared in Gloeothece cultures just before the beginning of the dark period and were absent from cultures by the middle of the proceeding light period. In contrast levels of other proteins studied remained constant throughout a diurnal illumination period. Proteins detected using antisera to dinitrogenase reductase ADP-ribosyl transferase and dinitrogenase reductase activating glycohydrolase may be responsible for the interchange between the apparently modified and unmodified forms of dinitrogenase reductase in Gloeothece. The modified form, although found predominantly when nitrogenase activity is low or absent, has not been shown to be catalytically inactive. Radiolabel study revealed that only two other proteins apart from the nitrogenase components were synthesized during the dark period. One of these, an 45700 Mr protein, may be implicated in nitrogenase catabolism as inhibition of its synthesis prevents nitrogenase breakdown in vivo. Protease activity detected against azocasein during the initial light period is not affected by inhibition of protein synthesis and may represent proteolytic enzymes which catabolise nitrogenase breakdown products but not the complete enzyme. In vitro study revealed that Gloeothece extracts readily catabolise native nitrogenase proteins but did not degrade Klebsiella pneumoniae dinitrogenase reductase suggesting a certain degree of specificity in the initial enzyme(s) of the catabolic process. Catabolism of native nitrogenase was increased by aerobic conditions, which also irreversibly inhibited nitrogenase activity. Breakdown products of both nitrogenase components were observed in vitro but not in vivo. This suggests a cascade of proteolytic enzymes in vivo prevent build-up of intermediate products of nitrogenase breakdown.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available