Title page for ETD etd-71597-151248

Type of Document Master's Thesis
Author Kasap, Murat
Author's Email Address mkasap@vt.edu
URN etd-71597-151248
Title Hydrogenase of Clostridium acetobutylicum ATCC 824
Degree Master of Science
Department Biochemistry
Advisory Committee
Advisor Name Title
Gregory, Eugene M.
White, Robert H.
Chen, Jiann-Shin Committee Chair
  • solvent production
  • clostridium acetobutylicum
  • hydrogenase
Date of Defense 1997-08-04
Availability restricted
C. acetobutylicum is an anaerobic bacterium that produces

acetic and butyric acids, hydrogen gas, and carbon dioxide

during the exponential phase of growth. When the culture

pH is allowed to remain near 4.5, the metabolism switches

to the production of the neutral compounds (solvents) -

acetone, n-butanol, and ethanol. The two metabolic phases

are known as the acidogenic and solventogenic phases. The

enzyme hydrogenase plays an important role in this

bacterium because it converts excess reducing power into

hydrogen gas to maintain a balance in the

oxidation-reduction state in the cell. During

solventogenesis, additional reducing power is used in the

production of n-butanol and ethanol, which leaves excess

reducing power to be vented as hydrogen gas. There are

conflicting reports about the level of hydrogenase in

acidogenic and solventogenic cells. There is also evidence

that hydrogenase may consume too much reducing power

during solventogenensis that it actually decreases the

cell's capacity to produce solvents. The purpose of this

study was to examine the level of hydrogenase in acidogenic

and solventogenic cells and to search for clues that may

indicate the presence of multiple forms of hydrogenase in

C. acetobutylicum. Both the hydrogen-oxidation (uptake)

and the hydrogen-production (evolution) activities were

measured in this study. The level of hydrogenase was

found higher in acidogenic cells than in solventogenic

cells, but there was no difference in the molecular weight

of hydrogenase from these two types of cells. A significant

increase in the ratio of the hydrogen-uptake over the

hydrogen-evolution activity was observed in oxygen or

heat-treated cell extracts and in hydrogenase partially

purified on a DEAE-cellulose column. The results suggest

the presence of more than one type of hydrogenase in this

species or hydrogenase activities in the two directions may

be differentially altered. These possibilities will be

investigated in a future study.

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