Hiramatsu T, Fukagawa N K, Marchini J S, Cortiella J, Yu Y M, Chapman T E, Young V R
Laboratory of Human Nutrition, Massachusetts Institute of Technology, Cambridge 02139.
Am J Clin Nutr. 1994 Oct;60(4):525-33. doi: 10.1093/ajcn/60.4.525.
We investigated plasma methionine and cysteine kinetics in eight healthy adult men receiving for 6 d each of five L-amino acid diets supplying 13 mg methionine.kg-1.d-1 without cystine or 6.5 mg methionine.kg-1.d-1 plus 0, 5.2, 10.5, or 20.9 mg cystine.kg-1.d-1. On the morning of day 7, primed, constant intravenous infusions of L-[2H3-methyl, 1-13C]methionine and L-[3,3-2H]cysteine were given for 8 h (for the first 3 h subjects remained in a fasted state and for the next 5 h received small, equal meals at hourly intervals to achieve a fed state). Methionine and cysteine fluxes and rate of methionine oxidation were estimated from plasma methionine and cysteine labeling and 13C in expired air. Methionine oxidation declined (P < 0.05) with lowered methionine intake. Cysteine flux was similar across diets and dietary cystine did not affect tracer methionine oxidation. If there is a sparing effect of dietary cystine on the methionine requirement in adults, it probably takes place during the "first-pass" removal of these amino acids within the splanchnic region.
我们研究了8名健康成年男性的血浆蛋氨酸和半胱氨酸动力学，这些男性分别接受了五种L-氨基酸饮食，每种饮食持续6天，其中一种饮食提供13mg蛋氨酸·kg⁻¹·d⁻¹且不含胱氨酸，另外四种饮食分别提供6.5mg蛋氨酸·kg⁻¹·d⁻¹加上0、5.2、10.5或20.9mg胱氨酸·kg⁻¹·d⁻¹。在第7天早晨，静脉注射L-[²H₃-甲基，¹-¹³C]蛋氨酸和L-[³,³-²H]半胱氨酸进行预充量和持续静脉输注8小时（前3小时受试者保持禁食状态，接下来5小时每隔一小时给予少量等量餐食以达到进食状态）。根据血浆蛋氨酸和半胱氨酸标记以及呼出气体中的¹³C估算蛋氨酸和半胱氨酸通量以及蛋氨酸氧化速率。随着蛋氨酸摄入量降低，蛋氨酸氧化减少（P<0.05）。不同饮食的半胱氨酸通量相似，饮食中的胱氨酸不影响示踪剂蛋氨酸氧化。如果饮食中的胱氨酸对成年人蛋氨酸需求有节约效应，可能发生在内脏区域对这些氨基酸的“首过”清除过程中。
