Ka. Adams et Aj. Davis, Dietary protein concentration regulates the mRNA expression of chicken hepatic malic enzyme, J NUTR, 131(9), 2001, pp. 2269-2274
Chicken hepatic malic enzyme activity varies with dietary protein content.
The mechanisms responsible for this alteration in activity are unclear. In
a series of four experiments, broiler chicks were allowed free access for 1
.5, 3, 6 or 24 h to a low (13 g/100 g diet), basal (22 g/100 g diet) or hig
h (40 g/100 g diet) protein diet. The diets were isocaloric and had equal c
oncentrations of dietary fat. Hepatic malic enzyme mRNA expression and enzy
me activity as well as total liver lipid concentration were examined for ea
ch experimental duration. There were no differences in the expression of th
e mRNA for malic enzyme at 1.5 h, but at 3, 6 and 24 h, malic enzyme mRNA e
xpression was significantly (P < 0.05) reduced in chicks fed the high prote
in diet and significantly enhanced in chicks fed the low protein diet compa
red with chicks fed the basal diet. Hepatic malic enzyme activities and tot
al lipid concentration were not different among the chicks fed the differen
t diets at 1.5 and 3 h. At 6 and 24 h, malic enzyme activity and total live
r lipid concentration were both significantly greater in birds fed the low
protein diet compared with levels in the birds fed the other two diets. In
birds fed the high protein diet, malic enzyme activity and total liver lipi
d concentration were significantly reduced at 24 h compared with birds fed
the basal diet. In a final experiment, the observed differences in malic en
zyme mRNA expression at 6 h were confirmed when chicks were given access to
isocaloric diets with the same protein levels as the initial 4 experiments
, but with the dietary concentration of carbohydrate held constant. The res
ults suggest that previously observed alterations in the activity of malic
enzyme, which were correlated with dietary protein intake, are due to rapid
changes in the mRNA expression of this enzyme.