Eakin R T, Morgan L O
Biochem J. 1975 Dec;152(3):529-35. doi: 10.1042/bj1520529.
Neurospora crassa cytochrome C biosynthetically labelled with [S-Me-13C]methionine was prepared and analysed by 13C nuclear-magnetic-resonance spectroscopy. The methyl group of methionine is extensively incorporated into an N-trimethyl-lysine-72 residue arise from S-adenosylmethionine transmethylation, and that the methyl carbons of methionine residues are sufficiently close to the haem centre to experience chemical shifts from the ring currents of the tetrapyrrole pi electrons and broadening due to binding of methionine-80 with the haem, as well as interaction of the S-E113C]methyl groups with the paramagnetic iron centre. Although whole cells of the labelled Neurospora produced a 13C resonance at the expected position for the methionyl methyl group most of the methyl label was diverted into N-tetra-alkyl ammonium compounds. After an active state of growth these labelled N-methyl compounds appear, in the main, to be low-molecular-weight derivatives of choline which, if associated with membrane, are in a sufficiently fluid environment to have short rotational correlation times. During a subsequent dormant growth period these compounds become associated to some extent with relatively more immobile phases as a result of membrane binding or an increase in membrane rigidity.
制备了用[S-甲基-¹³C]甲硫氨酸进行生物合成标记的粗糙脉孢菌细胞色素C，并通过¹³C核磁共振光谱进行分析。甲硫氨酸的甲基广泛掺入由S-腺苷甲硫氨酸转甲基作用产生的N-三甲基赖氨酸-72残基中，并且甲硫氨酸残基的甲基碳足够靠近血红素中心，从而受到来自四吡咯π电子环电流的化学位移影响，以及由于甲硫氨酸-80与血红素结合而导致的谱线展宽，还有[S-E113C]甲基基团与顺磁性铁中心的相互作用。尽管标记的粗糙脉孢菌全细胞在甲硫氨酰甲基的预期位置产生了¹³C共振，但大部分甲基标记物都被转移到了N-四烷基铵化合物中。在活跃生长状态之后，这些标记的N-甲基化合物主要似乎是胆碱的低分子量衍生物，如果与膜相关，它们处于足够流动的环境中，具有较短的旋转相关时间。在随后的休眠生长阶段，由于膜结合或膜刚性增加，这些化合物在一定程度上与相对更不流动相相关联。
