Bujard E, Finot P A
Ann Nutr Aliment. 1978;32(2-3):291-305.
The classical methods to measure lysine availability give rise to some difficulties in milks due to the presence of deoxyketose-lysine (DOKL). Six methods, one of which measuring the blocked lysine, are studied. Amino acid chromatography gives a too high value of lysine when it is blocked as DOKL, the latter regenerating lysine during acid hydrolysis. The determined lysine does not correspond to the available one. Fluro-dinitro-benzene is not fully specific for free epsilon-NH2 of lysine and the reducing sugars present interfere during the reaction in converting "nitro" into "amino" groups. Guanidization is a specific reaction between the epsilon-NH2 of lysine and O-methyl-isourea with formation of homoarginine. The homarginine, calculated as lysine corresponds to the available lysine. Reduction with sodium borhydride converts the DOKL to a stable compound which, during acid hydrolysis, does not regenerate lysine and does not form furosine. The recovered lysine corresponds to the available one. Our "in vitro" digestion method with simultaneous dialysis enables the determination of available lysine, as the proteolytic enzymes used do not split up the DOKL binding. The liberated lysine corresponds to the available one. The blocked lysine is measured from furosine after acid hydrolysis. A formula, which makes up the level of furosine formation and for lysine regeneration from DOKL, is established.
由于存在脱氧酮糖赖氨酸（DOKL），经典的测定赖氨酸可利用性的方法在牛奶中会产生一些困难。研究了六种方法，其中一种用于测定被阻断的赖氨酸。当赖氨酸以DOKL形式被阻断时，氨基酸色谱法给出的赖氨酸值过高，因为DOKL在酸水解过程中会再生赖氨酸。所测定的赖氨酸与可利用的赖氨酸不对应。氟二硝基苯对赖氨酸的游离ε-NH2并非完全特异，并且存在的还原糖在将“硝基”转化为“氨基”基团的反应过程中会产生干扰。胍化是赖氨酸的ε-NH2与O-甲基异脲之间的特异性反应，会形成高精氨酸。以赖氨酸计算的高精氨酸对应于可利用的赖氨酸。用硼氢化钠还原可将DOKL转化为一种稳定的化合物，在酸水解过程中，该化合物不会再生赖氨酸，也不会形成糠氨酸。回收的赖氨酸对应于可利用的赖氨酸。我们的同时进行透析的“体外”消化方法能够测定可利用的赖氨酸，因为所使用的蛋白水解酶不会分解DOKL结合物。释放出的赖氨酸对应于可利用的赖氨酸。酸水解后，通过糠氨酸测定被阻断的赖氨酸。建立了一个公式，该公式考虑了糠氨酸的形成水平以及DOKL再生赖氨酸的情况。
