pH值、镁离子浓度对蓝隐藻藻蓝蛋白聚合状态影响的研究

Effect of pH Value and Mg^(2+) Concentration on Aggregation State of Phycocyanin in Chroomonas placiodea

从蓝隐藻(Chroomonas placoidea)中分离得到A_(645)/A_(280)>7的4种形式的藻蓝蛋白PC645,其相对分子质量相近,并呈现相似的吸收及荧光光谱特性.采用蔗糖密度梯度离心法,研究了80%硫铵沉淀所得PC645的聚合状态与pH值和镁离子浓度变化之间的关系.结果表明,单纯pH值变化对纯化后PC645的聚合状态有一定的影响,pH值在4.92~8.67范围内,酸性条件下PC645倾向于进一步聚合;而碱性pH值范围时PC645的异二聚体结构会出现解聚.镁离子浓度为0~50 mmol/L时,PC645状态基本不变,以异二聚体的形式为主;镁离子浓度达到100 mmol/L以上,PC645随着镁离子浓度的提高而出现一定比例的解聚.证明隐藻藻蓝蛋白在水溶液中可形成聚合程度不同的多种形式,且高聚合状态的PC645很可能对应于光合作用活性状态.实验结果将为今后进一步研究隐藻藻胆蛋白的结构、性质和功能提供依据.

Four forms of phycocyanin 645 samples,with A645/A280〉 7 and exhibiting similar molecular weight as well as absorptive and fluorescent characteristics,are isolated and purified from Chroomonas placoidea. The aggregation state of PC645 precipitated with 80% ammonium sulfate followed by the variation of pH value and magnesium ion concentration is investigated by using sucrose density gradient centrifugation. The results show that pH value changes have a certain effect on the aggregation state of purified PC645. In the pH value range of 4. 92-8. 67,the PC645 heterodimer tends to further aggregate under acidic conditions and dissociate in alkaline pH range. When the concentration of Mg2＋ is between 0-50 mmol/L,the aggregation degree of phycocyanin remains basically unchanged,where PC645 exists mainly in the form of heterodimer. When the concentration of Mg2＋ is above 100 mmol/L,a portion of phycocyanin heterodimer dissociates as Mg2＋ concentration increases. These results imply that phycocyanin may appear in different forms with different aggregation state in aqueous solution. Aggregation of PC645 is responded to the active state of photosynthesis. The results will provide aseful information for further study on the structure,properties and function of cryptophytic phycobiliprotein.