Adams E C, Weiss M R
Biochem J. 1969 Nov;115(3):441-7. doi: 10.1042/bj1150441.
Haptoglobin binds haemoglobin so firmly that there is practically no dissociation. It would be expected that the heat of the reaction would be relatively large. The development of the microcalorimeter by Benzinger offered the opportunity to measure the heat of reaction. The experiments were carried out in the Beckman 190B Microcalorimeter in two ways: (1) a constant amount of haptoglobin (Kabi; 65mg.) with different amounts of haemoglobin, and (2) a constant amount of haemoglobin (32.5mg.) with different amounts of haptoglobin. The proteins, each in 5ml. of 0.15m-phosphate buffer, pH7.4, were placed in equal-volume calorimeter cells. The heat produced/mg. of haemoglobin was calculated from the slope of the curve for a constant amount of haptoglobin and from the maximum heat for a constant amount of haemoglobin. This heat is about 70kcal./mole at 37 degrees . DeltaH varies with temperature, being -70.2 at 37 degrees , -29.7 at 20 degrees and 7.2 at 4 degrees . From the amount of haptoglobin required to attain maximum heat with 32.5mg. of haemoglobin and the amount of haemoglobin required to attain maximum heat with 65mg. of haptoglobin, it appears that at excess of haptoglobin there is competition between the reactions of 2moles of haptoglobin with 1mole of haemoglobin (or 2 alphabeta-chains) and 1mole of haptoglobin with 1mole of haemoglobin.
触珠蛋白与血红蛋白结合得非常牢固，几乎不存在解离。可以预期该反应的热量会相对较大。本津格发明的微量量热计提供了测量反应热的机会。实验在贝克曼190B型微量量热计中以两种方式进行：（1）固定量的触珠蛋白（卡比；65毫克）与不同量的血红蛋白，（2）固定量的血红蛋白（32.5毫克）与不同量的触珠蛋白。每种蛋白质都溶解在5毫升pH7.4的0.15摩尔磷酸盐缓冲液中，然后放入等体积的量热计样品池中。每毫克血红蛋白产生的热量是根据固定量触珠蛋白的曲线斜率以及固定量血红蛋白的最大热量计算得出的。在37摄氏度时，该热量约为70千卡/摩尔。焓变随温度变化，37摄氏度时为-70.2，20摄氏度时为-29.7，4摄氏度时为7.2。根据使32.5毫克血红蛋白达到最大热量所需的触珠蛋白量以及使65毫克触珠蛋白达到最大热量所需的血红蛋白量，似乎在触珠蛋白过量时，2摩尔触珠蛋白与1摩尔血红蛋白（或2条αβ链）的反应和1摩尔触珠蛋白与1摩尔血红蛋白的反应之间存在竞争。
