Bettendorff L, Wins P, Lesourd M
Laboratory of General and Comparative Biochemistry, University of Liège, Belgium.
Biochim Biophys Acta. 1994 May 26;1222(1):1-6. doi: 10.1016/0167-4889(94)90018-3.
The subcellular distribution of thiamine derivatives in rat brain was studied. Thiamine diphosphate content was highest in the mitochondrial and synaptosomal fractions, and lowest in microsomal, myelin and cytosolic fractions. Only 3-5% of total thiamine diphosphate was bound to transketolase, a cytosolic enzyme. Thiamine triphosphate was barely detectable in the microsomal and cytosolic fraction, but synaptosomes were slightly enriched in this compound compared to the crude homogenate. Both myelin and mitochondrial fractions contained significant amounts of thiamine triphosphate. In order to estimate the relative turnover rates of these compounds, the animals received an intraperitoneal injection of either [14C]thiamine or [14C]sulbutiamine (isobutyrylthiamine disulfide) 1 h before decapitation. The specific radioactivities of thiamine compounds found in the brain decreased in the order: thiamine > thiamine triphosphate > thiamine monophosphate > thiamine diphosphate. Incorporation of radioactivity into thiamine triphosphate was more marked with [14C]sulbutiamine than with [14C]thiamine. The highest specific radioactivity of thiamine diphosphate was found in the cytosolic fraction of the brain, though this pool represents less than 10% of total thiamine diphosphate. Cytosolic thiamine diphosphate had a twice higher specific radioactivity when [14C]sulbutiamine was used as precursor compared with thiamine though no significant differences were found in the other cellular compartments. Our results suggest the existence of two thiamine diphosphate pools: the bound cofactor pool is essentially mitochondrial and has a low turnover; a much smaller cytosolic pool (6-7% of total TDP) of high turnover is the likely precursor of thiamine triphosphate.
研究了硫胺素衍生物在大鼠脑内的亚细胞分布。硫胺素二磷酸含量在线粒体和突触体部分最高，在微粒体、髓磷脂和胞质部分最低。硫胺素二磷酸总量中只有3 - 5%与转酮醇酶（一种胞质酶）结合。硫胺素三磷酸在微粒体和胞质部分几乎检测不到，但与粗匀浆相比，突触体中该化合物略有富集。髓磷脂和线粒体部分都含有大量的硫胺素三磷酸。为了估计这些化合物的相对周转率，在断头前1小时给动物腹腔注射[¹⁴C]硫胺素或[¹⁴C]舒必利硫胺（异丁酰硫胺二硫化物）。脑内发现的硫胺素化合物的比放射性按以下顺序降低：硫胺素＞硫胺素三磷酸＞硫胺素单磷酸＞硫胺素二磷酸。与[¹⁴C]硫胺素相比，[¹⁴C]舒必利硫胺使放射性掺入硫胺素三磷酸的情况更明显。硫胺素二磷酸的最高比放射性出现在脑的胞质部分，尽管该部分仅占硫胺素二磷酸总量的不到10%。当使用[¹⁴C]舒必利硫胺作为前体时，胞质硫胺素二磷酸的比放射性是硫胺素的两倍，尽管在其他细胞区室未发现显著差异。我们的结果表明存在两个硫胺素二磷酸池：结合辅因子池主要在线粒体中，周转率低；一个周转快得多的较小的胞质池（占总硫胺素二磷酸的6 - 7%）可能是硫胺素三磷酸的前体。
