92
P. K. STUMPF AND G. A. BARBER
seedlings has unified these previous observations into a system whereby
a fatty acid (C M ) is first peroxidatively decarboxylated into the C n _i
aldehyde and C0 2 . The aldehyde is oxidized by a DPN specific dehydrogenase to a \^γι-ι aci d which then undergoes a repeat of the cycle.
This is depicted in Fig. 3.
DPN
+
DPNH
FIG. 3. α-Oxidation of long-chain fatty acids. KEY: (I) long-chain fatty acid
peroxidase; (II) aldehyde dehydrogenase.
That the peroxidase oxidation plays a definite role in fatty acid
metabolism in plants is indicated by the observation that in the release
of carboxyl carbon in a mitochondrial preparation half of the total
oxidation is catalyzed by the peroxidase while the remainder is related
to the classic ^-oxidation system. The role of the system in the cell is
however obscure. Fatty aldehydes occur as even carbon chain compounds and are probably formed by the reduction of a thioester by an
enzyme similar to that of Burtom and Stadtman which reduces acetylCoA to acetaldehyde (54).
In both these systems there is no conventional method for trapping
the available energy. Further research in this area should bring into
sharper focus the role of these systems in the plant cell.
IV. Mechanism of Odd-Chain Fatty Acid Oxidation
Although propionic acid undergoes several transformations in the
cell, for several years investigators thought that the primary attack was
by α-oxidation via the sequence propionate —> acrylate -» lactate —> pyruvate. No real support for this reaction sequence could be furnished. In
fact, much evidence from sheep rumen organisms, propionic acid bacteria, Micrococcus lactiiyticus, and green photosynthesizing bacteria indicated a close relationship between succinate and propionic acid and
carbon dioxide (55). The metabolism of odd-chain fatty acids can now
be described in rather precise terms and reveals three distinct pathways:
P. K. STUMPF AND G. A. BARBER
seedlings has unified these previous observations into a system whereby
a fatty acid (C M ) is first peroxidatively decarboxylated into the C n _i
aldehyde and C0 2 . The aldehyde is oxidized by a DPN specific dehydrogenase to a \^γι-ι aci d which then undergoes a repeat of the cycle.
This is depicted in Fig. 3.
DPN
+
DPNH
FIG. 3. α-Oxidation of long-chain fatty acids. KEY: (I) long-chain fatty acid
peroxidase; (II) aldehyde dehydrogenase.
That the peroxidase oxidation plays a definite role in fatty acid
metabolism in plants is indicated by the observation that in the release
of carboxyl carbon in a mitochondrial preparation half of the total
oxidation is catalyzed by the peroxidase while the remainder is related
to the classic ^-oxidation system. The role of the system in the cell is
however obscure. Fatty aldehydes occur as even carbon chain compounds and are probably formed by the reduction of a thioester by an
enzyme similar to that of Burtom and Stadtman which reduces acetylCoA to acetaldehyde (54).
In both these systems there is no conventional method for trapping
the available energy. Further research in this area should bring into
sharper focus the role of these systems in the plant cell.
IV. Mechanism of Odd-Chain Fatty Acid Oxidation
Although propionic acid undergoes several transformations in the
cell, for several years investigators thought that the primary attack was
by α-oxidation via the sequence propionate —> acrylate -» lactate —> pyruvate. No real support for this reaction sequence could be furnished. In
fact, much evidence from sheep rumen organisms, propionic acid bacteria, Micrococcus lactiiyticus, and green photosynthesizing bacteria indicated a close relationship between succinate and propionic acid and
carbon dioxide (55). The metabolism of odd-chain fatty acids can now
be described in rather precise terms and reveals three distinct pathways: