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Glycine and serine catabolism in non‐photosynthetic higher plant cells: their role in C1 metabolism
Author(s) -
Mouillon JeanMarie,
Aubert Serge,
Bourguig Jacques,
Gout Elisabeth,
Douce Roland,
Rébeillé Fabrice
Publication year - 1999
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.1999.00591.x
Subject(s) - serine hydroxymethyltransferase , catabolism , glycine , serine , biochemistry , glycine cleavage system , metabolism , amino acid , biosynthesis , methionine , cytosol , chemistry , biology , enzyme
Summary Glycine and serine are two interconvertible amino acids that play an important role in C1 metabolism. Using 13 C NMR and various 13 C‐labelled substrates, we studied the catabolism of each of these amino acids in non‐photosynthetic sycamore cambial cells. On one hand, we observed a rapid glycine catabolism that involved glycine oxidation by the mitochondrial glycine decarboxylase (GDC) system. The methylenetetra‐ hydrofolate (CH 2 ‐THF) produced during this reaction did not equilibrate with the overall CH 2 ‐THF pool, but was almost totally recycled by the mitochondrial serine hydroxymethyltransferase (SHMT) for the synthesis of one serine from a second molecule of glycine. Glycine, in contrast to serine, was a poor source of C1 units for the synthesis of methionine. On the other hand, catabolism of serine was about three times lower than catabolism of glycine. Part of this catabolism presumably involved the glycolytic pathway. However, the largest part (about two‐thirds) involved serine‐to‐glycine conversion by cytosolic SHMT, then glycine oxidation by GDC. The availability of cytosolic THF for the initial SHMT reaction is possibly the limiting factor of this catabolic pathway. These data support the view that serine catabolism in plants is essentially connected to C1 metabolism. The glycine formed during this process is rapidly oxidized by the mitochondrial GDC–SHMT enzymatic system, which is therefore required in all plant tissues.