Sil Susmita, Chakraborti Abhay Sankar
Department of Biophysics, Molecular Biology and Genetics, University College of Science, Kolkata, India.
Mol Cell Biochem. 2002 Aug;237(1-2):103-10. doi: 10.1023/a:1016595402925.
The binding parameters of hematoporphyrin, a photosensitizing drug used in photodynamic therapy, interacting with myoglobin, an oxygen storage protein, have been studied spectrofluorometrically and spectrophotometrically. Two concentration ranges of hematoporphyrin, representing significantly monomeric and aggregated (dimeric) states have been used. The binding affinity constant (K) decreases and the possible number of binding sites (p) increases as the porphyrin changes from significantly monomeric state to predominantly dimeric state. Titration of the protein with hematoporphyrin in a spectrophotometric study (differential spectroscopy) exhibits an isosbestic point indicating a ground state complex formation. The interaction leads to a conformational change of the protein as observed in a circular dichroism study. The hematoporphyrin-myoglobin interaction causes oxygen release from the protein and it varies with the stoichiometric ratio of the porphyrin:protein. Hematoporphyrin also increases the myoglobin-catalysed hydrogen peroxide-mediated oxidation of o-dianisidine and NADH. These findings on the effects of hematoporphrin-myoglobin interaction should be given due consideration in therapeutic uses of the porphyrin and its derivatives.
采用荧光光谱法和分光光度法研究了用于光动力疗法的光敏药物血卟啉与氧储存蛋白肌红蛋白相互作用的结合参数。使用了两个血卟啉浓度范围，分别代表显著的单体状态和聚集（二聚体）状态。随着卟啉从显著的单体状态转变为主要的二聚体状态，结合亲和常数（K）降低，可能的结合位点数（p）增加。在分光光度研究（差示光谱法）中用卟啉滴定蛋白质显示出等吸收点，表明形成了基态复合物。如圆二色性研究中所观察到的，这种相互作用导致蛋白质的构象变化。血卟啉 - 肌红蛋白相互作用导致蛋白质释放氧气，并且它随卟啉与蛋白质的化学计量比而变化。血卟啉还增加了肌红蛋白催化的过氧化氢介导的邻联茴香胺和NADH的氧化。在卟啉及其衍生物的治疗用途中，应适当考虑这些关于血卟啉 - 肌红蛋白相互作用影响的发现。
