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Open Access Thesis


Plant enzymes.; Soybean;


Azide ion is a mechanism-based inactivator of a number of peroxidases. However, there are often variations in the manner in which inactivation occurs. Soybean Peroxidase (SBP) is found in the plant's seed coat. Unlike many other peroxidases, a single enzyme rather than several isozymes are produced thus making more simple the purification and characterization of the enzyme. In this research it was shown that, as with other peroxidases, SBP is inactivated by azide during turnover. During azide oxidation SBP forms a ferrous-NO intermediate. In this respect, SBP is similar to the lignin peroxidases from Phanerochaete chrysosporium which also form ferrous-NO complexes as reaction intermediates. In contrast, horseradish peroxidase does not form a stable ferrous-NO complex. Of interest is the observation that, as long as a peroxidase remains in the ferrous-NO form it is resistant to inactivation. The SBP ferrous-NO complex is less stable than the ferrous-NO complex formed by lignin peroxidases.

Kinetic analysis revealed that inactivation was time and concentration dependent. The dissociation constant (K1) for SBP and azide was shown to be 1.05 mM. The pseudo-first order rate constant for inactivation (Kinact) was 0.06 sec-1 and t1/2 for inactivation was 12.2 sec. Azide did not inactivate SBP in the absence of hydrogen peroxide, a required oxidizing cosubstrate. Inactivation was irreversible and the heme moiety was destroyed during turnover.

Year of Submission


Degree Name

Master of Science


Department of Chemistry and Biochemistry


Department of Chemistry


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Date Original


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