摘要
对于卡尔文循环的调控机理,多数学者认为:①FDPase,SDPase 和 Ru5PK 是ATP 和 NADPH 产生驱动作用的位点;②[CO_2]/[O_2]通过增强 Rubjsco 的羧化活性而促进CO_2同化。本文用数学模型证明第一个假设是错误的,而仅由后一个假设也不能解释 CO_2对卡尔文循环的促进作用。作者根据对数学模型的分析补充两个假设:①ATP 的驱动位点是在输出反应之中而不在循环内部;②RuBP 对输出反应有反馈抑制。据此计算出的调控规律与实验相符。这说明在卡尔文循环中尚有未被发现的调控机理。
A mathematical model is proposed to examine the validity of current hypotheses about the regulatory mechanisms in photosynthesis.It is a system of equations based upon well accepted knowledge about the Calvin cycle.The kinetic properties of Ru5PK,FDPase and SDPase are especially expressed according to the known experimental facts.Regulatorybebaviours of the photosynthetic system under different environmental conditions can be obtained from the steady state solutlon of the model.Important contradictions between simulation and experiments are found: 1)The influence of CO_2/O_2 ratio upon the output flux of the Calvin cycle is negative,instead of positive as expected. 2)The level of ATP or NADPH has a negative regulatory influence on the output flux of the Calvin cycle. 3)The influence of the activity of Ru5PK,SDPase and FDPase is negetive and weak. An approximate analytical solution to the Calvin cycle clearly shows that these unexpected behayviours are inherent properties of the structure of the network.It implies that there must be some unknown regulatory mechanisms in the Calvin cycle.New hypotheses are proposed which put the driving site of ATP on the output reactions,and introduce a feedback inhibitanee of RuBP upon output flux.They give results fit well with experimental facts,but verification by direct experiments is needed.
关键词
光合作用
卡尔文循环
调控机理
photosynthesis
Calvin cycle
regulatory mechanism
mathematical model
