Hus-Citharel A, Levillain O, Morel F
Laboratoire de Physiologie Cellulaire, CNRS, URA 219, Collège de France, Paris.
Pflugers Arch. 1995 Feb;429(4):485-93. doi: 10.1007/BF00704153.
The distribution of arginine synthase and arginase activities along the successive nephron segments of Meriones kidney was measured in vitro with single tubule enzymatic microtechniques making use of either L-[ureido-14C] Citrulline (0.108 mM) or L-[guanidino-14C]arginine (0.2 mM) as the respective substrates. Arginase activity (fmol urea formed per min per mm of tubule) was very low (5-25 fmol.min-1.mm-1) in most nephron segments including the early portions of proximal convoluted tubules (early PCT). It increased progressively after 3 mm of the PCT to reach a value of 200 fmol.min-1.mm-1 in the cortical portion of the straight proximal tubule (CPST), with a further increase, along the pars recta, of up to 250 fmol.min-1.mm-1 in the outer medullary portion (OSPST). In addition, arginase activity in OSPST and the adjacent descending thin limb (DTL) was higher in juxtamedullary nephrons (JN) than in the corresponding portions of superficial nephrons (SN). Arginine synthase activity (fmol arginine formed per mm of tubule per min) was present in proximal tubules exclusively, with a gradient decreasing along the PCT (about 600 fmol.min-1.mm-1 in the 1st mm, 65 fmol.min-1.mm-1 in CPST and 30 fmol.min-1.mm-1 in OSPST). It has been checked that CPST and OSPST (where the two enzyme systems are present) are able to convert citrulline directly into urea with a yield of 65%.(ABSTRACT TRUNCATED AT 250 WORDS)
利用单肾小管酶微技术，以L-[脲基-¹⁴C]瓜氨酸（0.108 mM）或L-[胍基-¹⁴C]精氨酸（0.2 mM）作为各自的底物，在体外测量了长爪沙鼠肾脏连续肾单位各节段中精氨酸合成酶和精氨酸酶的活性分布。在包括近端曲管（早期PCT）早期部分在内的大多数肾单位节段中，精氨酸酶活性（每毫米肾小管每分钟形成的尿素飞摩尔数）非常低（5 - 25飞摩尔·分钟⁻¹·毫米⁻¹）。在PCT的3毫米之后，其活性逐渐增加，在近端直小管（CPST）的皮质部分达到200飞摩尔·分钟⁻¹·毫米⁻¹的值，沿着直部进一步增加，在外髓部分（OSPST）高达250飞摩尔·分钟⁻¹·毫米⁻¹。此外，近髓肾单位（JN）的OSPST和相邻的降支细段（DTL）中的精氨酸酶活性高于浅表肾单位（SN）的相应部分。精氨酸合成酶活性（每毫米肾小管每分钟形成的精氨酸飞摩尔数）仅存在于近端小管中，沿PCT呈梯度下降（在第1毫米处约为600飞摩尔·分钟⁻¹·毫米⁻¹，在CPST中为65飞摩尔·分钟⁻¹·毫米⁻¹，在OSPST中为30飞摩尔·分钟⁻¹·毫米⁻¹）。已经证实，CPST和OSPST（存在两种酶系统的部位）能够将瓜氨酸直接转化为尿素，产率为65%。（摘要截取自250字）
