ALDIMINE TO KETOAMINE ISOMERIZATION (AMADORI REARRANGEMENT) POTENTIAL AT THE INDIVIDUAL NONENZYMIC GLYCATION SITES OF HEMOGLOBIN-A - PREFERENTIAL INHIBITION OF GLYCATION BY NUCLEOPHILES AT SITES OF LOW ISOMERIZATION POTENTIAL
ALDIMINE TO KETOAMINE ISOMERIZATION (AMADORI REARRANGEMENT) POTENTIAL AT THE INDIVIDUAL NONENZYMIC GLYCATION SITES OF HEMOGLOBIN-A - PREFERENTIAL INHIBITION OF GLYCATION BY NUCLEOPHILES AT SITES OF LOW ISOMERIZATION POTENTIAL
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DOI：
10.1007/bf01025633
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发表时间：
1991-06-01
期刊：
影响因子：
--
通讯作者：
DORAI, B
中科院分区：
文献类型：
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作者：
ACHARYA, AS;ROY, RP;DORAI, B
研究了血红蛋白A非酶糖基化位点的两个结构方面的相对作用，即氨基形成醛二胺加合物的难易程度和各自醛亚胺促进Amadori重排的微环境的倾向，这两个方面决定了醛三糖非酶糖基化位点的选择性。血红蛋白A的氨基在体外与醛三糖还原糖基化的化学反应活性与非还原模式下的不同。血红蛋白A的氨基对还原糖基化的反应性(即形成乙二胺的倾向)按Val-1(β)、Val-1(α)、Lys-66(β)、Lys-61(Alpha)和Lys-16(Alpha)的顺序降低。血红蛋白A对非还原糖基化的总反应性按Lys-16(α)、Val-1(β)、Lys-66(β)、Lys-82(β)、Lys-61(α)和Val-1(α)的顺序递减。由于乙二胺是还原和非还原修饰的共同中间体，蛋白质对这两种糖基化模式的不同选择性清楚地反映了非酶糖基化位点微环境促进异构化反应(即Amadori重排)的倾向。通过比较各个糖基化位点的非还原(非酶)和还原修饰，获得了对非酶糖化位点微环境倾向性的半定量估计。Lys-16(α)的微环境对重排非常有效，其相对效率按Lys-16(α)、Lys-82(β)、Lys-66(β)、Lys-61(α)、Val-1(β)和Val-1(α)的顺序递减。Lys-16(α)的微环境促进乙二胺Amadori重排的倾向性比Val-1(α)高约3个数量级，比Val-1(β)高约50倍。各个位点的非酶糖化程度受各种因素的调节，如pH、醛三糖的浓度和蛋白质的浓度。亲核试剂--如三、甘氨酸乙酯和氨基胍--通过捕获醛三糖来抑制糖基化。亲核试剂的非酶糖基化抑制能力与其生成乙二胺的倾向直接相关。因此，亲核试剂对给定位点上非酶糖基化的抑制程度直接反映了该位点上PK-α在决定该位点糖化作用中的相对作用。蛋白质氨基的非酶糖基化是一个相加/协同的结果，一方面是该位点形成乙二胺加合物的倾向，另一方面是它的微环境促进乙二胺异构化为酮胺的倾向。微环境的异构化潜能在决定蛋白质非酶糖化的位点特异性中起主导作用。
The relative roles of the two structural aspects of nonenzymic glycation sites of hemoglobin A, namely the ease with which the amino groups could form the aldimine adducts and the propensity of the microenvironments of the respective aldimines to facilitate the Amadori rearrangement, in dictating the site selectivity of nonenzymic glycation with aldotriose has been investigated. The chemical reactivity of the amino groups of hemoglobin A for in vitro reductive glycation with aldotriose is distinct from that in the nonreductive mode. The reactivity of amino groups of hemoglobin A toward reductive glycation (i.e., propensity for aldimine formation) decreases in the order Val-1(beta), Val-1(alpha), Lys-66(beta), Lys-61(alpha) and Lys-16(alpha). The overall reactivity of hemoglobin A toward nonreductive glycation decreased in the order Lys-16(alpha), Val-1(beta), Lys-66(beta), Lys-82(beta), Lys-61(alpha), and Val-1(alpha). Since the aldimine is the common intermediate for both the reductive and nonreductive modification, the differential selectivity of protein for the two modes of glycation is clearly a reflection of the propensity of the microenvironments of nonenzymic glycation sites to facilitate the isomerization reaction (i.e., Amadori rearrangement). A semiquantitative estimate of this propensity of the microenvironment of the nonenzymic glycation sites has been obtained by comparing the nonreductive (nonenzymic) and reductive modification at individual glycation sites. The microenvironment of Lys-16(alpha) is very efficient in facilitating the rearrangement and the relative efficiency decreases in the order Lys-16(alpha), Lys-82(beta), Lys-66(beta), Lys-61(alpha), Val-1(beta), and Val-1(alpha). The propensity of the microenvironment of Lys-16(alpha) to facilitate the Amadori rearrangement of the aldimine is about three orders of magnitude higher than that of Val-1(alpha) and is about 50 times higher than that of Val-1(beta). The extent of nonenzymic glycation at the individual sites is modulated by various factors, such as the pH, concentration of aldotriose, and the concentration of the protein. The nucleophiles-such as tris, glycine ethyl ester, and amino guanidine-inhibit the glycation by trapping the aldotriose. The nonenzymic glycation inhibitory power of nucleophile is directly related to its propensity to form aldimine. Thus, the extent of inhibition of nonenzymic glycation at a given site by a nucleophile directly reflects the relative role of pK-alpha of the site in dictating the glycation at that site. The nonenzymic glycation of an amino group of a protein is an additive/synergestic consequence of the propensity of the site to form aldimine adducts on one hand, and the propensity of its microenvironment to facilitate the isomerization of the aldimines to ketoamines on the other. The isomerization potential of microenvironment plays the dominant role in dictating the site specificity of the nonenzymic glycation of proteins.