Pratap J V, Ravishankar R, Vijayan M
Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560-012, India.
Acta Crystallogr B. 2000 Aug;56(Pt 4):690-6. doi: 10.1107/s0108768100002202.
The crystal structures of complexes of maleic acid with L-histidine and L-lysine have been determined. The two crystallographically independent amino acid molecules in the L-histidine complex have different closed conformations, while the lysine molecule in its complex has the most favourable conformation sterically with an all-trans sidechain trans to the alpha-carboxylate group. The maleic acid molecules exist as semi-maleate ions of similar conformation and contain a symmetric O...H...O hydrogen bond. Amino acid cations and semi-maleate anions aggregate into alternate layers in both the structures. The arrangement of molecules in the histidine layer in L-histidine semi-maleate is closer to that in the crystals of the free amino acid than in other L-histidine complexes. On the other hand, the arrangement of lysine molecules in its semi-maleate complex is different from any observed so far. However, the well established characteristic interaction patterns involving amino and carboxylate groups still play a major role in holding the molecules together in the crystal of the complex.
已测定马来酸与L-组氨酸和L-赖氨酸配合物的晶体结构。L-组氨酸配合物中两个晶体学独立的氨基酸分子具有不同的封闭构象，而其配合物中的赖氨酸分子具有空间上最有利的构象，其全反式侧链与α-羧基处于反式。马来酸分子以构象相似的半马来酸根离子形式存在，并含有对称的O…H…O氢键。在这两种结构中，氨基酸阳离子和半马来酸根阴离子聚集成交替的层。L-组氨酸半马来酸盐中组氨酸层的分子排列比其他L-组氨酸配合物更接近游离氨基酸晶体中的排列。另一方面，赖氨酸分子在其半马来酸盐配合物中的排列与迄今观察到的任何排列都不同。然而，涉及氨基和羧基的已确立的特征相互作用模式在配合物晶体中将分子结合在一起方面仍然起着主要作用。
