van der Westhuyzen J, van Tonder S V, Gibson J E, Kilroe-Smith T A, Metz J
Br J Nutr. 1985 May;53(3):657-62. doi: 10.1079/bjn19850075.
The effect of methylcobalamin inactivation by the gas nitrous oxide on plasma amino acid and tissue methionine levels in fruit bats (Rousettus aegyptiacus) was examined. Animals exposed to N2O-oxygen (1:1, v/v) for 90 min daily received a fruit diet with or without methionine or betaine supplements. Exposure and diets were continued for up to 17 weeks or until neurological impairment and muscular weakness was established. All the groups exposed to N2O had significantly lower liver, brain and plasma methionine concentrations except the methionine-supplemented animals which showed significantly raised levels. Plasma homocysteine, which was absent in controls, was present in all the N2O-exposed groups. Betaine supplementation resulted in reduced accumulation of homocysteine in plasma. However, plasma and liver methionine levels were only slightly increased compared with animals on the basal diet, and brain methionine levels were the lowest of all the groups studied. These results support the hypothesis that reduced methionine synthesis is an important contributor to the development of neurological impairment in this species and suggest that dietary supplementation with the methionine precursor betaine cannot replace the loss of vitamin B12-dependent methionine synthesis.
研究了一氧化二氮气体对埃及果蝠（Rousettus aegyptiacus）血浆氨基酸和组织蛋氨酸水平的甲基钴胺素失活作用。每天暴露于一氧化二氮-氧气（1:1，体积/体积）90分钟的动物，喂食含或不含蛋氨酸或甜菜碱补充剂的水果饮食。暴露和饮食持续长达17周，或直至出现神经功能障碍和肌肉无力。除补充蛋氨酸的动物蛋氨酸水平显著升高外，所有暴露于一氧化二氮的组肝脏、大脑和血浆中的蛋氨酸浓度均显著降低。对照组中不存在的血浆同型半胱氨酸在所有暴露于一氧化二氮的组中均有出现。补充甜菜碱可减少血浆中同型半胱氨酸的积累。然而，与基础饮食组动物相比，血浆和肝脏中的蛋氨酸水平仅略有升高，且大脑中的蛋氨酸水平是所有研究组中最低的。这些结果支持以下假设：蛋氨酸合成减少是该物种神经功能障碍发展的一个重要因素，并表明用蛋氨酸前体甜菜碱进行饮食补充不能替代维生素B12依赖的蛋氨酸合成的损失。
