Oppezzo O J, Fernandez H N
Institute of Chemistry and Biophysical Chemistry (UBA-CONICET), Buenos Aires, Argentina.
Int J Pept Protein Res. 1991 Apr;37(4):277-82. doi: 10.1111/j.1399-3011.1991.tb00740.x.
The presence of tyrosine residues in the contact area between protomers of bovine somatotropin dimers (Fernandez & Delfino, Biochem. J. 209, 107-115, 1983) was investigated taking advantage of the impaired self-associating ability of molecules iodinated at such residues. Reaction of bovine somatotropin dissolved in 8 M urea with the NaI-Chloramine T couple (2.1 x 10(-4) M) rendered a preparation with 3.1 iodine atoms per molecule which, by stepwise elimination of the denaturant and gel filtration through Sephadex G-100, originated two distinguishable populations: one able (iododerivatives I), the other unable (iododerivatives II) to self-associate. After frontal analysis, iododerivatives II were found to be unable to interact even with native molecules. Identification of the reacting tyrosine residues indicated that iodination of tyrosine 142 was responsible for the loss of the ability to form dimers in iododerivatives II. Iodohormones retained the ability to bind to somatogenic mouse hepatocyte receptors--the relative potency for iododerivatives I and II being 0.60 (0.34-1.03) and 0.71 (0.41-1.22) respectively.
利用在这些残基处碘化的分子自缔合能力受损的特点，研究了牛生长激素二聚体原体之间接触区域中酪氨酸残基的存在情况。将溶解于8M尿素中的牛生长激素与NaI - 氯胺T对（2.1×10⁻⁴M）反应，得到每分子含有3.1个碘原子的制剂，通过逐步去除变性剂并经葡聚糖G - 100凝胶过滤，产生了两个可区分的群体：一个能够自缔合（碘衍生物I），另一个不能自缔合（碘衍生物II）。经过前沿分析，发现碘衍生物II甚至不能与天然分子相互作用。对反应性酪氨酸残基的鉴定表明，酪氨酸142的碘化导致碘衍生物II中形成二聚体的能力丧失。碘激素保留了与促生长小鼠肝细胞受体结合的能力——碘衍生物I和II的相对效力分别为0.60（0.34 - 1.03）和0.71（0.41 - 1.22）。
