Effetto dei Ritardanti di Crescita Sulla Fosforilazione Ossidativa e Sulla Fotofosforilazione Ciclica. II

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Abstract
Effects of growth retardants on oxidative phosphorylation and on cyclic photophosphorylation. The effects of some growth retardants on energy interconversion mechanisms has been studied. It has been reported that Amo 1618 and CCC greatly inhibit oxidative phosphorylation in isolated pea mitochondria. The inhibition of Pi esterification is higher than the oxygen uptake using succinate; this suggests a weak uncoupling effect. However substituting succinate with malate the inhibition of oxygen consuption approaches that of Pi esterification so that the uncoupling effect is quite dubious. On the other hand Amo 1618 does not stimulate oxygen uptake of mitochondria in « state 4 ». For this reason it is not possible to consider growth retardants definitely uncoupling agents, as Heatherbell et al. suggest, and it will be necessary to clarify this point using more appropriate techniques. It has been reported that Amo 1618 and CCC do not inhibit cyclic photophosphorylation with phenazine or FMN in isolated spinach chloroplasts. The data suggest that oxidative phosphorylation inhibition is a peculiar characteristic of growth retardants. The inhibitory effect on oxidative phosphorylation is obtained with concentrations lower than the « in vivo » concentrations required to produce the typical effects of growth retardants. The possibility that the action of growth retardants « in vivo » is due to the lowering of ATP in the cell in relation to the inhibition of Pi esterification has been discussed.