Haverberg L N, Omstedt P T, Munro H N, Young V R
Biochim Biophys Acta. 1975 Sep 9;405(1):67-71. doi: 10.1016/0005-2795(75)90315-3.
In order to use Ntau-methylhistidine (3-methylhistidine) excretion in the urine as a measure of muscle protein breakdown, it is necessary to demonstrate that other tissues are not important sources of this protein constituent. Accordingly, the concentration of Ntau-methylhistidine in blood serum and in the mixed proteins of heart, brain, lung, kidney, diaphragm, spleen, testis, stomach, liver and hind leg skeletal muscle was measured in male rats of approx. 400 g body weight. The free Ntau-methylhistidine concentration of rat serum was less than 2 nmol per ml. In contrast, measurable amounts of Ntau-methylhistidine were found in the mixed proteins of all tissues and organs examined. The highest concentration was found in skeletal muscle (658 nmol/g tissue). Assuming muscle mass to be 45% of body weight, it has been estimated that the muscle contains more than ten times the total amount of this amino acid present in all of the other organs analyzed, which together account for about 20% of total body weight. These findings indicate that skeletal muscle is likely to be the major source of urinary Ntau-methylhistidine and the latter is, in consequence, a reflection of myofibrillar protein breakdown in skeletal muscle.
为了将尿中Nτ-甲基组氨酸（3-甲基组氨酸）的排泄量作为肌肉蛋白分解的衡量指标，有必要证明其他组织并非该蛋白质成分的重要来源。因此，对体重约400克的雄性大鼠血清以及心脏、大脑、肺、肾脏、膈肌、脾脏、睾丸、胃、肝脏和后肢骨骼肌的混合蛋白中Nτ-甲基组氨酸的浓度进行了测定。大鼠血清中游离Nτ-甲基组氨酸的浓度低于每毫升2纳摩尔。相比之下，在所检测的所有组织和器官的混合蛋白中均发现了可测量量的Nτ-甲基组氨酸。骨骼肌中的浓度最高（658纳摩尔/克组织）。假设肌肉质量占体重的45%，据估计，肌肉中该氨基酸的总量是所有其他分析器官中该氨基酸总量的十倍以上，而这些其他器官的重量约占体重的20%。这些发现表明，骨骼肌可能是尿中Nτ-甲基组氨酸的主要来源，因此，尿中Nτ-甲基组氨酸是骨骼肌中肌原纤维蛋白分解的反映。
