Viscardi R M, McKenna M C
Department of Pediatrics, University of Maryland School of Medicine, Baltimore.
Life Sci. 1994;54(19):1411-21. doi: 10.1016/0024-3205(94)00596-6.
Cholinephosphate cytidylyltransferase is the rate-limiting enzyme in the choline pathway of phosphatidylcholine synthesis in fetal and adult lung. To examine the developmental changes in cytidylyltransferase activity, subcellular fractions were prepared from freshly isolated type II cells from 19 and 21 d gestation fetal rats, newborn (0 h, 3 h, 3-12 h, +1, +2, +7 postnatal day), and adult rats and the fractions assayed for cytidylyltransferase activity. Cytidylyltransferase activity per cell was low during late fetal gestation, but rose rapidly during the first 3 h after birth, predominantly due to an increase in microsomal enzyme activity. Microsomal and cytosolic enzyme specific activity increased 6 and 3.9 fold, respectively, from birth (0 h) to +1 postnatal day. The subcellular distribution of enzyme activity changed from 40% microsomal in fetal type II cells to 85% microsomal at 3-12 h, and 60% in this compartment in adult type II cells. Although evidence suggests that membrane lipid may affect enzyme activity, developmental changes in type II cell membrane phospholipid fatty acid composition have not been previously studied. Capillary gas chromatography analysis of phospholipid fatty acids extracted from microsome fractions revealed a 3-fold increase in both total saturated and unsaturated phospholipid fatty acids from day 19 to day 21 gestation. There was a further 62% increase in total saturated fatty acids during the first postnatal day, concomitant with the peak in microsomal cytidylyltransferase activity.
胆碱磷酸胞苷转移酶是胎儿和成年肺脏中磷脂酰胆碱合成胆碱途径的限速酶。为了研究胞苷转移酶活性的发育变化，从妊娠19天和21天的胎鼠、新生鼠（出生后0小时、3小时、3 - 12小时、出生后第1天、第2天、第7天）以及成年大鼠新鲜分离的II型细胞中制备亚细胞组分，并对这些组分进行胞苷转移酶活性测定。每个细胞的胞苷转移酶活性在胎儿后期较低，但在出生后的前3小时迅速上升，主要是由于微粒体酶活性增加。从出生（0小时）到出生后第1天，微粒体和胞质酶的比活性分别增加了6倍和3.9倍。酶活性的亚细胞分布从胎儿II型细胞中40%为微粒体，变为出生后3 - 12小时85%为微粒体，成年II型细胞中该部分为60%。尽管有证据表明膜脂可能影响酶活性，但此前尚未研究过II型细胞膜磷脂脂肪酸组成的发育变化。对从微粒体组分中提取的磷脂脂肪酸进行毛细管气相色谱分析发现，从妊娠第19天到第21天，总饱和和不饱和磷脂脂肪酸均增加了3倍。在出生后的第一天，总饱和脂肪酸进一步增加了62%，与微粒体胞苷转移酶活性的峰值同时出现。
