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The bacterial-like lactate shuttle components from heterotrophic Euglena gracilis
Ricardo Jasso-Chávez1, Israel García-Cano, Alvaro Marín-Hernández
1Departamento de Bioquímica, Instituto Nacional de Cardiología, Juan Badiano #1, Col. Sección XVI, Tlalpan, México, D. F. 14080, México. rjassoch@aol.com
Biochimica Et Biophysica Acta
|August 23, 2005
Summary
This study analyzes Euglena gracilis lactate shuttle enzymes, revealing unique mitochondrial and cytosolic lactate dehydrogenases with potential bacterial origins. These findings shed light on lactate metabolism diversity.
Area of Science:
- Biochemistry
- Enzymology
- Microbial Metabolism
Background:
- The lactate shuttle system facilitates lactate transport and metabolism in various organisms.
- Euglena gracilis, a heterotrophic protist, possesses a complex system for lactate processing.
- Understanding these enzymes is crucial for elucidating metabolic pathways and evolutionary relationships.
Purpose of the Study:
- To structurally and kinetically characterize the lactate shuttle components in Euglena gracilis.
- To investigate the properties of mitochondrial and cytosolic lactate dehydrogenases.
- To explore potential evolutionary links between Euglena gracilis and bacterial lactate dehydrogenases.
Main Methods:
- Purification of mitochondrial membrane-bound NAD(+)-independent d-lactate dehydrogenase (d-iLDH) using CHAPS and heat treatment.
- Enzyme activity assays, including substrate specificity and inhibition studies.
- Affinity chromatography to identify and characterize cytosolic NAD(+)-dependent lactate dehydrogenases (d-nLDH and l-nLDH).
- Kinetic mechanism determination using ordered bi-bi models.
Main Results:
- Purified d-iLDH is a 62-kDa monomer with FAD cofactor, specific for d-lactate, and reduces quinones.
- Mitochondrial l-iLDH also reduces quinones but is unstable; both iLDHs are flavoproteins.
- Cytosolic fraction contains d-nLDH and l-nLDH tetramers with distinct kinetic properties.
- d-nLDH shows product inhibition, while l-nLDH is activated by fructose-1,6-bisphosphate, K(+), or NH4(+).
Conclusions:
- Euglena gracilis possesses unique lactate dehydrogenase enzymes with similarities to bacterial counterparts.
- The presence of quinone reductase activity in mitochondrial LDH and FBP-activated l-nLDH suggests a potential common evolutionary origin with bacteria.
- These findings contribute to understanding the diversity of lactate metabolism and enzyme evolution.