生命起源中的对称性破缺

Asymmetry in the Origin of Life

生命起源中的对称性破缺——生物分子手性均一性，是生命科学中的长期未解之谜。自然界中组成蛋白质的２０种氨基酸（除甘氨酸无不对称碳原子外）全部是Ｌ型，组成ＲＮＡ，ＤＮＡ中的核糖却全部是Ｄ型。对蛋白质和核酸的手性、分子构型（Ｄ和Ｌ）和旋光（＋和－，右旋光和左旋光）概念作了阐明。对当前国际上最著名的两大学说—β粒子极化和手性分子的相互作用与萨拉姆假说以及国内外的研究工作，结合科研组１０几年来的实验研究和理论观点作了较为全面的评述。

The first unifying principle in biochemistry is that the key moleculcs amino acids, sugars have the same handedness or chirality. Chiral molecules and their corresponding mirror images may be defined by left ( L )or right ( D ) optical rotatory dispersion. All living systems translate their genes into proteins composed of 20 L amino acids (except glycine). Like proteins, the nucleic acids DNA and RNA exist in nature in only one chirality composed of D configuration of 2 deoxyribose and ribose monomers. This phenomenon occurs when molecules are asymmetric. The cause for the great preference in life for L amino acids and D sugars over their corresponding enantiomers has been extensively studied. Based on a series of experiments of our research, it is found that elementary particles interact differentially with enantiomers of amino acids. The difference, though very small, could be detected by sensitive methods when the system is far from equilibrium at low temperature (77 K) but it could not cause macroscopic excess of one particular enantiomer without an effective amplification mechanism. Based on Salam's hypothesis, studies show that an obvious λ transition at (270±1)K occurred while measuring the specific heat of D and L valine and alanine by differential scanning calorimetry (DSC) in the temperature region of 77￣300 K,with the C pvalues of D form greater than that of L form. Magnetization measurement of single crystals of D,L alanine and D valine on SQUID magnetometer show that magnetic transition temperature coincident with that of λ transition. Temperatrue dependence of the X ray powder diffraction for D valine showed no crystal lattice change under the temperature cooling down from 293 K to 123 K. We propose that the difference of the magnetic susceptibility χ￣T curve between D and L forms of alanine and valine attributed to the variation of intramolecular geometry of chiral density in the presence of an external magnetic field. Such observations as magnetic susceptibility of molecules in single crystal amino acids is the first to be monitored.