Date of Award:

2016

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Chemistry and Biochemistry

Advisor/Chair:

Edwin Antony

Abstract

Photosynthesis is a fundamental biological process that sustains life on earth. Chlorophyll is the pigment that captures sunlight and converts it to chemical energy through photosynthesis. These essential light-harvesting compounds are found in photosynthetic plants, cyanobacteria, green algae, angiosperms and gymnosperms. In the chlorophyll biosynthetic pathway, protochlorophyllide (Pchlide) serves as the precursor molecule for chlorophyll. Protochlorophyllide oxidoreductases are a class of enzymes that catalyze the conversion of Pchlide to chlorophyllide a (Chlide), which subsequently is reduced and modified to form chlorophyll. A light-dependent protochlorophyllide oxidoreductase (LPOR) is found in flowering plants (angiosperms), and as the name suggests, requires the energy from light to catalyze the conversion. An unrelated dark- operative light-independent version (DPOR - dark-operative protochlorophyllide oxidoreductase) is found in cyanobacteria, photosynthetic bacteria, green algae and gymnosperms. DPOR functions in the absence of light, or low-light conditions and in the absence of oxygen. DPOR is a multi-subunit complex consisting of the BchL, BchN and BchB proteins which share striking structural similarities to the Nif proteins in the nitrogenase complex. ATP binding and hydrolysis is an essential aspect of DPOR catalysis, though it still remains mysterious as to how the energy from ATP is used to drive substrate reduction. The role of ATP in the conversion of Pchlide to Chlide has been examined kinetically to establish when ATP is hydrolyzed in the catalytic mechanism. Additionally, variants of the BchL protein have been developed to include a functional linked BchL homodimer, as well as Walker A mutated forms on one, or both ATPase sites of the protein. The data suggest a dynamic mechanism in which the binding and hydrolysis of both ATP are required for normal function.

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