Bettendorff L, Michel-Cahay C, Grandfils C, De Rycker C, Schoffeniels E
J Neurochem. 1987 Aug;49(2):495-502. doi: 10.1111/j.1471-4159.1987.tb02891.x.
The main electric organ of Electrophorus electricus is particularly rich in thiamine triphosphate, which represents 87% of the total thiamine content in this tissue. The thiamine pyrophosphate concentration, however, is very low in the eel electric organ and skeletal muscle as compared with other eel or rat tissues. Furthermore, electroplax membranes contain a whole set of enzymes responsible for the dephosphorylation of thiamine tri-, pyro- and monophosphate. Thiamine triphosphatase has a pH optimum of 6.8 and is dependent on Mg2+. The real substrate of the enzyme is probably a 1:1 complex of Mg2+ and thiamine triphosphate. Thiamine pyrophosphatase is activated by Ca2+. The apparent Km for thiamine triphosphate and Vmax are found to be, respectively, 1.76 mM and 5.95 nmol/mg of protein/min. Thiamine triphosphatase activity is inhibited at physiological K+ concentrations (up to 90 mM) and increasing Na+ concentrations (50% inhibition at 300 mM). ZnCl2 (10 mM) inhibits 90% of the enzyme activity. ATP and ITP are also strongly inhibitory. No significant effect of neurotoxins is seen. Membrane-associated thiamine triphosphatase is affected differently by proteolytic enzymes and is partially inactivated by pretreatment with phospholipase C and neuraminidase. The physiological significance of thiamine triphosphatase is discussed in relation to a specific role of thiamine in the nervous system.
电鳗的主要发电器官中硫胺三磷酸含量特别丰富，占该组织硫胺总量的87%。然而，与其他鳗鱼或大鼠组织相比，鳗鱼发电器官和骨骼肌中的硫胺焦磷酸浓度非常低。此外，电板膜含有一整套负责硫胺三磷酸、焦磷酸和单磷酸去磷酸化的酶。硫胺三磷酸酶的最适pH值为6.8，依赖于Mg2+。该酶的真正底物可能是Mg2+与硫胺三磷酸的1:1复合物。硫胺焦磷酸酶被Ca2+激活。硫胺三磷酸的表观Km和Vmax分别为1.76 mM和5.95 nmol/mg蛋白质/分钟。硫胺三磷酸酶活性在生理K+浓度（高达90 mM）和Na+浓度增加时受到抑制（在300 mM时抑制50%）。ZnCl2（10 mM）抑制90%的酶活性。ATP和ITP也有强烈的抑制作用。未观察到神经毒素有显著影响。膜相关硫胺三磷酸酶受蛋白水解酶的影响不同，经磷脂酶C和神经氨酸酶预处理后会部分失活。本文结合硫胺在神经系统中的特定作用讨论了硫胺三磷酸酶的生理意义。
