Poole J R, Mudd S H, Conerly E B, Edwards W A
J Clin Invest. 1975 May;55(5):1033-48. doi: 10.1172/JCI108004.
Apparent nitrogen balances and urinary sulfur excretions were determined for normal subjects, seven cystathionine synthase-deficient patients, and a single cystathioninuric patient on semisynthetic diets containing low-adequate amounts of methionine and very low amounts of methionine and very low amounts (12 mg daily, or less) of cystine. The amounts of supplemental cystine required to prevent abnormally high nitrogen or sulfur losses were determined. The five cystathionine synthase-deficient patients who had low residual activities of this enzyme detected in fibroblast and/or liver extracts did not lose more nitrogen or sulfur on diets virtually devoid of cystine than did the normal subjects. These results suggest that the widely expressed opinion that cystine is an essential amino acid for cystathionine syntase-deficient patients requires modification. Residual enzyme activity of only a few percent of normal may obviate such a cystine requirement. These results are compatible with, and lend support to, the working hypothesis which states that the pyridoxine response in cystathionine synthase-deficient patients is mediated by an increase in the residual activity of the affected enzyme.
对正常受试者、7名胱硫醚合成酶缺乏症患者和1名单纯胱硫醚尿症患者进行了表观氮平衡和尿硫排泄量的测定，这些受试者食用的是含低适量蛋氨酸、极低量蛋氨酸以及极少量（每日12毫克或更少）胱氨酸的半合成饮食。确定了预防异常高的氮或硫损失所需的补充胱氨酸量。在成纤维细胞和/或肝脏提取物中检测到该酶残留活性较低的5名胱硫醚合成酶缺乏症患者，在几乎不含胱氨酸的饮食中，其氮或硫的损失并不比正常受试者多。这些结果表明，关于胱氨酸是胱硫醚合成酶缺乏症患者必需氨基酸的广泛观点需要修正。仅为正常水平百分之几的残留酶活性可能消除对胱氨酸的这种需求。这些结果与工作假说相符并支持该假说，该假说认为胱硫醚合成酶缺乏症患者对吡哆醇的反应是由受影响酶的残留活性增加介导的。
