94
P. K. STUMPF AND G. A. BARBER
dently Reaction 6 is absent in animal tissues, since there is no evidence
of propionic acid undergoing this complete sequence [Reactions (i)(vii)].
C. BACTERIAL PATHWAY
(56b)
Oxidation of propionate by extracts of C. kluyveri involves the following series of reactions:
(i). Acetyl phosphate + Co A +± Acetyl-CoA + P»
(ii). Acetyl-CoA + Propionate <=* Propionyl-CoA + Acetate
(iii). Propionyl-CoA <± Acrylyl-CoA + 2 H
(iv). Acrylyl-CoA + H 2 0 <=±/3-Hydroxypropionyl-CoA
(v). ß-Hydroxypropionyl-CoA + TPN
+± Malonyl semialdehyde-CoA + TPNH + H
(vi). Malonyl semialdehyde-CoA + TPN <=* Malonyl-CoA + TPNH + H
(vii). Malony 1-CoA <=± Acetyl-CoA + C0 2
Note that while this series of reactions resembles the plant system,
the most important differences are Reactions (i), (ii), and (v). In
plant material Reaction (iv), the deacylation of ß-hydroxypropionylCoA, is essential. In addition acetyl-CoA enters the Krebs cycle pathway, whereas in the C. kluyveri system it undergoes condensation presumably to higher fatty acids or serves to activate other fatty acid by
Reaction (ii).
Reactions (i) to (iii) also occur in extracts of C. propionicum. In
addition ß-alanine-CoA is formed by the amination of ß-acrylyl-CoA
in the presence of a specific enzyme, acrylyl-CoA aminase.
V. Fatty Acid Oxidation — Comparative Aspects
A. ANAEROBIC BACTERIA
The remarkable ubiquity of certain metabolic patters has been elegantly demonstrated by the studies of fatty acid metabolism in the
anaerobic bacterium, Clostridium kluyveri. This organism, isolated from
the mud of a lake bottom (57), is an obligate anaerobe which secures
energy for its growth through the oxidation of ethanol, certainly an
aberrant way of life by ordinary standards. Yet the study of this obscure species has provided much of the basis of the understanding of
fat metabolism throughout the plant and animal kingdoms.
The over-all conversions effected by C. kluyveri were worked out by
Bornstein and Barker a number of years ago (58, 59), and the details
of those conversions have been investigated intensively since then. The
P. K. STUMPF AND G. A. BARBER
dently Reaction 6 is absent in animal tissues, since there is no evidence
of propionic acid undergoing this complete sequence [Reactions (i)(vii)].
C. BACTERIAL PATHWAY
(56b)
Oxidation of propionate by extracts of C. kluyveri involves the following series of reactions:
(i). Acetyl phosphate + Co A +± Acetyl-CoA + P»
(ii). Acetyl-CoA + Propionate <=* Propionyl-CoA + Acetate
(iii). Propionyl-CoA <± Acrylyl-CoA + 2 H
(iv). Acrylyl-CoA + H 2 0 <=±/3-Hydroxypropionyl-CoA
(v). ß-Hydroxypropionyl-CoA + TPN
+± Malonyl semialdehyde-CoA + TPNH + H
(vi). Malonyl semialdehyde-CoA + TPN <=* Malonyl-CoA + TPNH + H
(vii). Malony 1-CoA <=± Acetyl-CoA + C0 2
Note that while this series of reactions resembles the plant system,
the most important differences are Reactions (i), (ii), and (v). In
plant material Reaction (iv), the deacylation of ß-hydroxypropionylCoA, is essential. In addition acetyl-CoA enters the Krebs cycle pathway, whereas in the C. kluyveri system it undergoes condensation presumably to higher fatty acids or serves to activate other fatty acid by
Reaction (ii).
Reactions (i) to (iii) also occur in extracts of C. propionicum. In
addition ß-alanine-CoA is formed by the amination of ß-acrylyl-CoA
in the presence of a specific enzyme, acrylyl-CoA aminase.
V. Fatty Acid Oxidation — Comparative Aspects
A. ANAEROBIC BACTERIA
The remarkable ubiquity of certain metabolic patters has been elegantly demonstrated by the studies of fatty acid metabolism in the
anaerobic bacterium, Clostridium kluyveri. This organism, isolated from
the mud of a lake bottom (57), is an obligate anaerobe which secures
energy for its growth through the oxidation of ethanol, certainly an
aberrant way of life by ordinary standards. Yet the study of this obscure species has provided much of the basis of the understanding of
fat metabolism throughout the plant and animal kingdoms.
The over-all conversions effected by C. kluyveri were worked out by
Bornstein and Barker a number of years ago (58, 59), and the details
of those conversions have been investigated intensively since then. The