Slovacek R E, Crowther D, Hind G
Biochim Biophys Acta. 1980 Oct 3;592(3):495-505. doi: 10.1016/0005-2728(80)90094-8.
Evolution of oxygen and turnover of cytochromes b-563 and f were measured upon illumination of isolated intact spinach chloroplasts with a series of flashes. The flash yield of cytochrome f oxidation approximated the sum of the yields of cytochrome b-563 reduction and electron transfer through Photosystem II, regardless of whether HCO(-3), 3-phosphoglycerate or O2 served as the terminal electron acceptor. No absorbance contribution form cytochrome b-559 was discerned within the time range studied. Some pseudocyclic electron flow occurred when both HCO(-3) and 3-phosphoglycerate were omitted, and possibly also during induction of photosynthesis; however, the flash yield data suggest tht O2 is not reduced at a significant rate during steady state photosynthesis. The maximum rate of cytochrome f turnover (1000 microequiv./mg chlorophyll per h) was adequate to support the highest rates of photosynthesis observed in isolated chloroplasts. These results agree with the concept that cytochrome f is a component both of the linear and cyclic pathways whereas cytochrome b-563 functions only in the cyclic pathway. NH4Cl decreased the half time of cytochrome b-563 oxidation fro 11.6 to 8.2 ms and decreased the half time of cytochrome f reduction from 7.2 to 2.8 ms. The cyclic and linear pathways thus seem to be jointly regulated by a transthylakoid H+ gradient through a common control point on the reducing side of cytochrome f. Cyclic turnover also increased during the induction phase of photosynthesis, when linear throughput is limited by the rate of utilization of NADPH. The slow rise in the P-518 transient correlated with increased cyclic activity under the above conditions. It is proposed that flexibility in the utilization of linear and cyclic pathways allows the chloroplast to generate ATP and NADPH in ratios appropriate to varying needs.
用一系列闪光照射分离的完整菠菜叶绿体时，测定了氧气的释放以及细胞色素b - 563和f的周转情况。无论HCO₃⁻、3 - 磷酸甘油酸还是O₂作为末端电子受体，细胞色素f氧化的闪光产额都近似于细胞色素b - 563还原和通过光系统II的电子传递产额之和。在所研究的时间范围内，未检测到细胞色素b - 559的吸光度贡献。当省略HCO₃⁻和3 - 磷酸甘油酸时会发生一些假循环电子流，在光合作用诱导过程中可能也会发生；然而，闪光产额数据表明，在稳态光合作用期间，O₂不会以显著速率被还原。细胞色素f周转的最大速率（每小时1000微当量/毫克叶绿素）足以支持在分离叶绿体中观察到的最高光合作用速率。这些结果与细胞色素f是线性和循环途径的组成部分，而细胞色素b - 563仅在循环途径中起作用的概念一致。NH₄Cl将细胞色素b - 563氧化的半衰期从11.6毫秒降至8.2毫秒，并将细胞色素f还原的半衰期从7.2毫秒降至2.8毫秒。因此，循环和线性途径似乎通过细胞色素f还原侧的一个共同控制点，由跨类囊体H⁺梯度共同调节。在光合作用的诱导阶段，当线性通量受NADPH利用速率限制时，循环周转也会增加。在上述条件下，P - 518瞬态的缓慢上升与循环活性增加相关。有人提出，线性和循环途径利用的灵活性使叶绿体能够以适合不同需求的比例生成ATP和NADPH。
