Albi Elisabetta, Lazzarini Remo, Magni Mariapia Viola
Department of Biochemical Sciences and Molecular Biotechnology, Physiopathology, Policlinico Monteluce, 06100 Perugia, Italy.
FEBS Lett. 2003 Aug 14;549(1-3):152-6. doi: 10.1016/s0014-5793(03)00810-x.
The chromatin phospholipid fraction is enriched in sphingomyelin content which changes during cell maturation and proliferation. Recently, we have demonstrated that the sphingomyelin variations can be due to chromatin neutral sphingomyelinase and sphingomyelin-synthase activities which differ in pH and K(m) optima from those present in nuclear membranes. The sphingomyelin can be used also as a source of phosphorylcholine for phosphatidylcholine synthesis by reverse sphingomyelin-synthase. In the present work we have studied the possible existence of reverse sphingomyelin-synthase activity in nuclear membrane and chromatin. A very low activity was detected in the homogenate, cytosol and nuclear membrane (0.93+/-0.14, 2.61+/-0.33 and 0.87+/-0.13 pmol/mg protein/min, respectively), whereas the activity present in chromatin was 37.09+/-2.05 pmol/mg protein/min. The reverse sphingomyelin-synthase decreases the intranuclear diacylglycerol pool and increases the intranuclear ceramide pool, whereas sphingomyelin-synthase has an opposite effect. The possible correlation between these enzymes is discussed.
染色质磷脂组分富含鞘磷脂，其含量在细胞成熟和增殖过程中会发生变化。最近，我们已经证明鞘磷脂的变化可能归因于染色质中性鞘磷脂酶和鞘磷脂合成酶的活性，它们在pH值和米氏常数（Km）最适值方面与核膜中的酶不同。鞘磷脂还可以作为磷酸胆碱的来源，通过反向鞘磷脂合成酶参与磷脂酰胆碱的合成。在本研究中，我们探讨了核膜和染色质中可能存在的反向鞘磷脂合成酶活性。在匀浆、胞质溶胶和核膜中检测到的活性非常低（分别为0.93±0.14、2.61±0.33和0.87±0.13 pmol/mg蛋白/分钟），而染色质中的活性为37.09±2.05 pmol/mg蛋白/分钟。反向鞘磷脂合成酶会减少核内二酰甘油池，增加核内神经酰胺池，而鞘磷脂合成酶则具有相反的作用。本文还讨论了这些酶之间可能存在的相关性。
