The mechanism of mitochondrial maturation in the liver of the perinatal rat.

cations is also difficult to test, as their presence is essential for the interaction of phytohaemagglutinin with its membrane receptors (Kay, 1971 ; Lindahl-Kiessling, 1972). The observation that the Caz+ ionophore A231 87 is itself a lymphocyte mitogen (Maino et al., 1974) lends strong support to the hypothesis that the rate of CaZ+ uptake may be of crucial importance, but the results presented here show that most of the reported increases in membrane transport are not part of the key activation sequence, and that many of them are quite irrelevant.