Maekawa S, Hibasami H, Uji Y, Nakashima K
Department of Biochemistry, Mie University School of Medicine, Japan.
Biochim Biophys Acta. 1989 Dec 8;993(2-3):199-203. doi: 10.1016/0304-4165(89)90164-5.
Putrescine, spermidine and spermine were transported into the rat lens against a concentration gradient. This process appeared to be energy-dependent and involved a carrier system different from those for amino acids. Competition experiments suggested that the three polyamines were transported by the same system or very similar systems. Incorporated spermine was converted to spermidine and putrescine, and spermidine was converted to putrescine. In contrast, the conversion of putrescine to spermidine and spermine, or the conversion of spermidine to spermine was not observed. Furthermore, ornithine was not utilized for the synthesis of putrescine. These metabolic characteristics of the polyamines in the rat lens were correlated with the extremely low activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase. Other enzymes of polyamine metabolisms, however, were relatively active. In conclusion, the lens has a very low ability for the de novo synthesis of polyamines. The polyamines in the lens are considered to be supplied form the surrounding intraocular fluid by an active transport system specific for polyamines.
腐胺、亚精胺和精胺逆浓度梯度转运进入大鼠晶状体。这一过程似乎依赖能量，且涉及一种与氨基酸转运系统不同的载体系统。竞争实验表明，这三种多胺是通过相同的系统或非常相似的系统进行转运的。摄入的精胺会转化为亚精胺和腐胺，亚精胺会转化为腐胺。相反，未观察到腐胺转化为亚精胺和精胺，或亚精胺转化为精胺的情况。此外，鸟氨酸未用于腐胺的合成。大鼠晶状体中多胺的这些代谢特征与鸟氨酸脱羧酶和S-腺苷甲硫氨酸脱羧酶的极低活性相关。然而，多胺代谢的其他酶相对活跃。总之，晶状体从头合成多胺的能力非常低。晶状体中的多胺被认为是通过一种对多胺具有特异性的主动转运系统从周围的眼内液中供应的。
