Plant Protochlorophyllide Oxidoreductases A and B: CATALYTIC EFFICIENCY AND INITIAL REACTION STEPS

The enzyme protochlorophyllide oxidoreductase (POR, EC 1.3.1.33) has a key role in plant development. It catalyzes one of the later steps in chlorophyll synthesis, the light-induced reduction of protochlorophyllide (PChlide) into chlorophyllide (Chlide) in the presence of NADPH. Two isozymes of plan...

Full description

Saved in:
Bibliographic Details
Published in:The Journal of biological chemistry 2015-11, Vol.290 (47), p.28530-28539
Main Authors: Garrone, Alessio, Archipowa, Nataliya, Zipfel, Peter F, Hermann, Gudrun, Dietzek, Benjamin
Format: Article
Language:English
Subjects:
Biocatalysis
Chlorophyll - biosynthesis
Cyanobacteria - enzymology
Cyanobacteria - metabolism
Enzymology
Hordeum - enzymology
Oxidoreductases - metabolism
Protein Binding
Protochlorophyllide - metabolism
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The enzyme protochlorophyllide oxidoreductase (POR, EC 1.3.1.33) has a key role in plant development. It catalyzes one of the later steps in chlorophyll synthesis, the light-induced reduction of protochlorophyllide (PChlide) into chlorophyllide (Chlide) in the presence of NADPH. Two isozymes of plant POR, POR A and POR B from barley, which differ in their function during plant life, are compared with respect to their substrate binding affinity, catalytic efficiency, and catalytic mechanism. POR B as compared with POR A shows an 5-fold higher binding affinity for PChlide and an about 6-fold higher catalytic efficiency measured as kcat/Km. Based on the reaction intermediates, which can be trapped at low temperatures the same reaction mechanism operates in both POR A and POR B. In contrast to results reported for POR enzymes from cyanobacteria, the initial light-driven step, which occurs at temperatures below 180 K already involves the full chemistry of the photoreduction and yields the reaction product, Chlide, in an enzyme-bound form. The subsequent dark reactions, which include cofactor (NADP(+)) release and cofactor (NADPH) rebinding, show different temperature dependences for POR A and POR B and suggest a higher conformational flexibility of POR B in the surrounding active center. Both the higher substrate binding affinity and well adapted enzyme dynamics are held responsible for the increased catalytic activity of POR B as compared with POR A.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M115.663161