The interference between the effects of various nucleotides and lipids on the Hill reaction of chloroplasts was studied at the various stages of aging. The presence of nucleotides such as ATP, ADP and AMP inhibits not only Hill activity of freshly prepared chloroplasts without phosphorylating reagents but that of chloroplasts aged at low temperature. However, the nucleotides act as a stimulator for chloroplasts aged for the long period over about 75 hrs. Hill activity is lowered by the presence of the lipids extracted from the aged chloroplast suspension, but when the nucleotides are added, recovered to a large extent. The lowering of Hill activity due to the aging can be understood by the adsorption effect of free lipids (containing free fatty acids) released from chloroplasts on the lamellae membrane. For this reason, in the case of chloroplasts freshly prepared or aged for the short period, nucleotides may can directly attack to destruct the membrane structure of lamellae, leading to the inhibition of Hill activity. In the case of chloroplasts aged for the long period, the free lipids may form the adsorption layer on the lamellae membrane enough to cause the inhibition of Hill activity. Such an adsorption layer may be removed to some extent by the addition of nucleotides, and the lamellae membrane may come back to more active state. The controlling of the adsorption of the lipids is understood to be derived from the direct interaction of nucleotide with fatty acid. This expiains the observed inhibition and stimulation effects of nucleotides, depending on the aging period, on the Hill reaction of aged chloroplasts.
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