Cunningham V J, Hay L, Stoner H B
Biochem J. 1975 Mar;146(3):653-8. doi: 10.1042/bj1460653.
Bovine, human and rat serum albumins were defatted and palmitic acid, oleic acid and lauric acid added in various molar ratios. The binding of L-tryptophan to these albumins was measured at 20 degrees C in a 0.138 M salt solution at pH 7.4, by using an ultrafiltration technique, and analysed in terms of n, the number of available tryptophan-binding sites per albumin molecule, with apparent association constant, k. 2. n and k were 0.90 and 2.3x10(-4)M(minus-1) respectively for defatted bovine serum albumin and 0.87 and 9.7x10(-3)M(-minus-1) for human albumin. Addition of palmitic acid did not decrease n until the molar ratio, fatty acid/bovine albumin, approached and exceeded 2. The decrease in k was small and progressive. In contrast, lauric caused a marked decrease in n and k at ratios as low as 0.5. A similar distinction between the effects on n of palmitic acid and oleic acid and those of lauric acid was seen for human albumin. k for human albumin was not significantly affected by fatty acids under the conditions studied. 3. It is concluded that primary long-chain fatty acid sites interact only weakly with the tryptophan site on albumin and that inhibition of tryptophan binding occurs when secondary long-chain sites are occupied. Primary medium-chain fatty acid sites are distinct from primary long-chain sites but may be grouped with secondary long-chain sites. 4. The relationship between free and bound tryptophan in samples of rat plasma (Stoner et al., 1975) is discussed in terms of a similar but limited study of rat albumin.
将牛、人及大鼠血清白蛋白脱脂，并按不同摩尔比添加棕榈酸、油酸和月桂酸。在20℃、pH 7.4的0.138 M盐溶液中，采用超滤技术测定L-色氨酸与这些白蛋白的结合，并根据每个白蛋白分子上可利用的色氨酸结合位点数量n以及表观缔合常数k进行分析。2. 脱脂牛血清白蛋白的n和k分别为0.90和2.3×10⁻⁴ M⁻¹，人白蛋白的n和k分别为0.87和9.7×10⁻³ M⁻¹。添加棕榈酸直到脂肪酸/牛白蛋白的摩尔比接近并超过2时，n才会降低。k的降低幅度较小且呈渐进性。相比之下，月桂酸在摩尔比低至0.5时就会导致n和k显著降低。对于人白蛋白，棕榈酸和油酸与月桂酸对n的影响也有类似差异。在所研究的条件下，脂肪酸对人白蛋白的k没有显著影响。3. 得出的结论是，主要的长链脂肪酸位点与白蛋白上的色氨酸位点相互作用较弱，当次要的长链位点被占据时，色氨酸结合会受到抑制。主要的中链脂肪酸位点与主要的长链脂肪酸位点不同，但可能与次要的长链脂肪酸位点归为一类。4. 根据对大鼠白蛋白的一项类似但有限的研究，讨论了大鼠血浆样本（斯托纳等人，1975年）中游离色氨酸与结合色氨酸之间的关系。
