| dc.description.abstract | NADP-linked malic enzyme has been considered part of a
lipogenic set of cytosol enzymes which includes the NADP-linked
HMP shunt dehydrogenases, CCE, acetyl CoA carboxylase and
fatty acid synthetase. In the present study, the activity of
NADP-linked dehydrogenases have been measured in selected tissues
from a variety of avian and mammalian species representing
different dietary and phylogenetic types. The pattern of distribution
of malic enzyme, G6PD and ICDH does not appear to be dependent
on the dietary habits of the species. In birds, however, a
difference emerges between two phylogenetic groups. In general,
all birds have a high liver malic enzyme activity; the passerines
have an enzyme activity many fold in excess of that of mammalian
liver. In some non-passerine liyers, however, malic enzyme
activity was nearer to that typycal .of mammals. G6PD was extremely .
inactive in all passerine livers examined, but it was present
in somewhat higher activities in livers of non-passerines.
In rat liver, malic enzyme and G6PD levels were highly
responsive to dietary manipulations, being elevated in conditions
favouring fatty acid synthesis and depressed in livers of
starved rats, whereas ICDH did not respond to such changes.
In pigeon liver, these enzymes were little affected by fasting
and refeeding. Malic enzymes were purified from rat and pigeon
liver by similar procedure and assayed under identical conditions.
Kinetically, the two enzymes were found to be similar.
Phenobarbitone, an inducer of microsomal drug metabolising
systems, caused a. substantial increase in the activity of hepatic
malic enzyme in normally fed rats and in rats in which the basic
level of the enzyme had been reduced by starvation or by feeding
the animal with a high protein diet, but not in animals where
the basic level had already been elevated by feeding a diet rich
in sucrose. Phenobarbitone had relatively little effect on
HMP shunt dehydrogenases, whereas methyl cholanthrene, a compound
which evokes an induction of microsomal drug metabolising systems
qualitatively different from that produced by phenobarbitone,
induced not only malic enzyme levels but also G6PD and 6PGD
significantly. ICDH and CCE were not affected by either of the
two compounds. | en |
