Borum P R, Broquist H P
J Biol Chem. 1977 Aug 25;252(16):5651-5.
The initial steps of carnitine biosynthesis in Neurospora crassa involve the methylation of the epsilon-amino group of lysine as follows: Lysine A leads to monomethyllysine B leads to dimethyllysine C leads to trimethyllysine. The methyl donor is S-adenosylmethionine. An enzyme, S-adenosylmethionine:epsilon-N-L-lysine methyltransferase, has been purified from N. crassa to near homogeneity as judged by column chromatography, polyacrylamide gel electrophoresis, and ultracentrifugation. This protein catalyzes all three methylation reactions. The reaction rates are: A less than B less than C. Sedimentation equilibrium and molecular filtration give a molecular weight of 22,000 for the protein. Sedimentation equilibrium analysis of the protein in 6 M guanidine hydrochloride and sodium dodecyl sulfate-polyacrylamide gel electrophoresis do not detect the possibility of subunit structure. The enzyme contains no half-cystine but does contain several acidic residues. The protein exhibits an absorption band between 400 and 420 nm which is 40 to 50 times less than the absorption seen at 280 nm and is not affected by the presence of substrates. The source of this absorption in unkown.
粗糙脉孢菌中肉碱生物合成的初始步骤涉及赖氨酸ε-氨基的甲基化，过程如下：赖氨酸A生成一甲基赖氨酸B，一甲基赖氨酸B生成二甲基赖氨酸C，二甲基赖氨酸C生成三甲基赖氨酸。甲基供体是S-腺苷甲硫氨酸。一种名为S-腺苷甲硫氨酸：ε-N-L-赖氨酸甲基转移酶的酶已从粗糙脉孢菌中纯化出来，通过柱色谱、聚丙烯酰胺凝胶电泳和超速离心判断，其纯度接近均一。这种蛋白质催化所有三个甲基化反应。反应速率为：A < B < C。沉降平衡和分子过滤测得该蛋白质的分子量为22,000。在6 M盐酸胍中对该蛋白质进行沉降平衡分析，以及进行十二烷基硫酸钠-聚丙烯酰胺凝胶电泳，均未检测到亚基结构的可能性。该酶不含半胱氨酸，但含有几个酸性残基。该蛋白质在400至420 nm之间呈现一条吸收带，其吸收强度比在280 nm处观察到的吸收低40至50倍，且不受底物存在的影响。这种吸收的来源尚不清楚。
