Reference "Mitochondria are a major site for folate and thymidylate synthesis in plants"

Reference ID

54995

Title

Mitochondria are a major site for folate and thymidylate synthesis in plants

Source

J Biol Chem, 1996, vol. 271, pp. 9466-9472

Authors (5)

Neuburger-M	Rebeille-F
Jourdain-A	Nakamura-S
Douce-R

Abstract

The subcellular distributions of folate and folate-synthesizing enzymes were
investigated in pea leaves. It was observed that the mitochondrial folate pool
(approximately 400 micron) represented approximately 50% of the total pool.
Furthermore, all the enzymes involved in tetrahydrofolate polyglutamate
synthesis were present in the mitochondria. In marked contrast, we failed to
detect any significant activity of these enzymes in chloroplasts, cytosol, and
nuclei. The presence of the tetrahydrofolate synthesis pathway in mitochondria
is apparently a general feature in plants since potato tuber mitochondria also
contained a high folate concentration (approximately 200 micron) and all the
enzymes required for tetrahydrofolate polyglutamate synthesis. The specific
activities of tetrahydrofolate-synthesizing enzymes were rather low (1.5-15 nmol
h-1 mg-1 matrix protein), except for dihydrofolate reductase (180-500 nmol h-1
mg-1 matrix protein). Dihydrofolate reductase was purified to homogeneity. The
enzyme had a native molecular mass of approximately 140 kDa and was constituted
of two identical 62-kDa subunits. Interestingly, this mitochondrial protein
appeared to be a bifunctional enzyme, also supporting thymidylate synthesis. The
cell distribution of thymidylate synthase was also investigated. No significant
activity was observed in cell fractions other than mitochondria, indicating that
plant cell mitochondria are also a major site for thymidylate synthesis.