Ku C P, Passow H
Biochim Biophys Acta. 1980 Jul 16;600(1):212-27. doi: 10.1016/0005-2736(80)90426-5.
The time course of creatine influx or efflux as measured in populations of red cells or red cell ghosts with normal age distribution does not follow simple two-compartment kinetics. This suggests that the contributions of individual cells to transport as measured in the populations as a whole are not uniform. In agreement with this inference, fractionation of red cell populations with respect to cell age shows that transport in young cells is considerably faster than in old cells. The dependence of creatine transport on creatine concentration in the medium follows an equation that can be interpreted to represent a super-imposition of a saturable component (apparent Km = 0.02 mM) and another component that cannot be saturated up to a creatine concentration of 5.0 mM. In contrast to the non-saturable component, the saturable component depends on the energy metabolism of the cell and can be inhibited by beta-guanidinopropionic acid and the proteolytic enzyme pronase. This latter finding suggests that the saturable component represents active transport that is mediated by a transport protein. The non-saturable component is little, if at all, dependent on cell age while the saturable component is higher in young cells than in old cells. Phloretin inhibits both components of creatine flux, but the maximal inhibition that can be achieved at high concentration is only 70--80%. Under the experimental conditions used for the study of creatine transport, creatinine equilibration between cells and medium follows the kinetics expected for a steady-state two-compartment system. Creatinine flux is proportional to creatine concentration over the concentration range studied (up to 5 mM). It cannot be inhibited by beta-guanidinopropionic acid or pronase.
在具有正常年龄分布的红细胞群体或红细胞影中所测量的肌酸流入或流出的时间进程并不遵循简单的两室动力学。这表明在整个群体中所测量的单个细胞对转运的贡献并不均匀。与这一推断一致的是，根据细胞年龄对红细胞群体进行分级分离显示，年轻细胞中的转运比老细胞中的转运要快得多。肌酸转运对培养基中肌酸浓度的依赖性遵循一个方程，该方程可以解释为代表一个可饱和成分（表观Km = 0.02 mM）和另一个在肌酸浓度高达5.0 mM时仍不可饱和的成分的叠加。与不可饱和成分相反，可饱和成分依赖于细胞的能量代谢，并且可以被β-胍基丙酸和蛋白水解酶链霉蛋白酶所抑制。后一个发现表明，可饱和成分代表由一种转运蛋白介导的主动转运。不可饱和成分几乎不依赖于细胞年龄，而可饱和成分在年轻细胞中比在老细胞中更高。根皮素抑制肌酸通量的两个成分，但在高浓度下所能达到的最大抑制率仅为70%-80%。在用于研究肌酸转运的实验条件下，细胞与培养基之间的肌酐平衡遵循稳态两室系统预期的动力学。在所研究的浓度范围内（高达5 mM），肌酐通量与肌酸浓度成正比。它不能被β-胍基丙酸或链霉蛋白酶所抑制。
