Hogarth C, Ellar D J
Biochem J. 1978 Oct 15;176(1):197-203. doi: 10.1042/bj1760197.
Accumulation of Ca2+ in Bacilli occurs during stages IV to VI of sporulation. Ca2+ uptake into the sporangium was investigated in Bacillus megaterium KM in protoplasts prepared in stage III of sporulation and cultured to continue sporulation. These protoplasts and whole cells exhibit essentially identical Ca2+ uptake, which is compared with that of forespores isolated in stage V of sporulation. Ca2+, uptake into both sporangial protoplasts and isolated forespores occurs by Ca2+-specific carrier-mediated processes. However, protoplasts exhibit a Km value of 31 micrometer, and forespores have a Km value of 2.1 mM. Sporangial protoplasts accumulate Ca2+ against a concentration gradient. In contrast, Ca2+ uptake into isolated forespores is consistent with downhill transfer in which both rate and extent of uptake are affected by the external Ca2+ concontration. Dipicolinic acid has no effect on Ca2+ uptake by isolated forespores, apart from decreasing the external Ca2+ concentration by chelation. A model for sporulation-specific Ca2+ accumulation is proposed, in which Ca2+ is transported into the sporangium, resulting in a concentration of 3--9 mM in the mother-cell cytoplasm. This high concentration of Ca2+ enables carrier-mediated transfer down a concentration gradient into the forespore compartment, where a low free Ca2+ concentration is maintained by complexing with dipicolinic acid.
芽孢杆菌中Ca2+的积累发生在芽孢形成的IV至VI阶段。在巨大芽孢杆菌KM中，对处于芽孢形成III阶段制备的原生质体进行研究，这些原生质体经培养继续进行芽孢形成，以此来研究Ca2+摄入到芽孢囊的情况。这些原生质体和完整细胞表现出基本相同的Ca2+摄取情况，并与在芽孢形成V阶段分离的前芽孢的Ca2+摄取情况进行比较。Ca2+通过Ca2+特异性载体介导的过程摄入到芽孢囊原生质体和分离的前芽孢中。然而，原生质体的Km值为31微米，前芽孢的Km值为2.1毫摩尔。芽孢囊原生质体逆浓度梯度积累Ca2+。相比之下，Ca2+摄入到分离的前芽孢中与顺浓度梯度转运一致，摄取的速率和程度都受外部Ca2+浓度的影响。除了通过螯合作用降低外部Ca2+浓度外，吡啶二羧酸对分离的前芽孢摄取Ca2+没有影响。提出了一个芽孢形成特异性Ca2+积累的模型，其中Ca2+被转运到芽孢囊中，导致母细胞细胞质中的浓度达到3-9毫摩尔。这种高浓度的Ca2+使得载体介导的Ca2+能够顺着浓度梯度转移到前芽孢区室，在前芽孢区室中，通过与吡啶二羧酸络合维持低游离Ca2+浓度。
