Adams K A, Davis A J
Department of Poultry Science, University of Georgia, Athens, 30602, USA.
J Nutr. 2001 Sep;131(9):2269-74. doi: 10.1093/jn/131.9.2269.
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 high (40 g/100 g diet) protein diet. The diets were isocaloric and had equal concentrations of dietary fat. Hepatic malic enzyme mRNA expression and enzyme activity as well as total liver lipid concentration were examined for each experimental duration. There were no differences in the expression of the mRNA for malic enzyme at 1.5 h, but at 3, 6 and 24 h, malic enzyme mRNA expression was significantly (P < 0.05) reduced in chicks fed the high protein diet and significantly enhanced in chicks fed the low protein diet compared with chicks fed the basal diet. Hepatic malic enzyme activities and total lipid concentration were not different among the chicks fed the different diets at 1.5 and 3 h. At 6 and 24 h, malic enzyme activity and total liver 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 lipid concentration were significantly reduced at 24 h compared with birds fed the basal diet. In a final experiment, the observed differences in malic enzyme 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 results 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.
鸡肝脏苹果酸酶活性随日粮蛋白质含量而变化。导致这种活性改变的机制尚不清楚。在一系列四个实验中，让肉鸡自由采食低蛋白（13 g/100 g日粮）、基础蛋白（22 g/100 g日粮）或高蛋白（40 g/100 g日粮）日粮1.5、3、6或24小时。日粮能量相等，日粮脂肪浓度相同。对每个实验持续时间检测肝脏苹果酸酶mRNA表达、酶活性以及肝脏总脂质浓度。在1.5小时时，苹果酸酶mRNA的表达没有差异，但在3、6和24小时时，与饲喂基础日粮的雏鸡相比，饲喂高蛋白日粮的雏鸡苹果酸酶mRNA表达显著降低（P<0.05），而饲喂低蛋白日粮的雏鸡苹果酸酶mRNA表达显著增强。在1.5和3小时时，饲喂不同日粮的雏鸡肝脏苹果酸酶活性和总脂质浓度没有差异。在6和24小时时，与饲喂其他两种日粮的鸡相比，饲喂低蛋白日粮的鸡的苹果酸酶活性和肝脏总脂质浓度均显著更高。在饲喂高蛋白日粮的鸡中，与饲喂基础日粮的鸡相比，24小时时苹果酸酶活性和肝脏总脂质浓度显著降低。在最后一个实验中，当雏鸡采食与最初4个实验蛋白质水平相同但碳水化合物日粮浓度保持恒定的等能量日粮时，证实了6小时时苹果酸酶mRNA表达的观察差异。结果表明，先前观察到的与日粮蛋白质摄入量相关的苹果酸酶活性变化是由于该酶mRNA表达的快速变化所致。
