Effect of Lead Arsenate on Citrate Synthase Activity in Fruit Pulp of Satsuma Mandarin

YAMAKI Yoshikazu T.

doi:10.2503/jjshs.58.899

The effects of lead arsenate on citrate synthase (CS) activity were examined in order to obtain information on the mechanism of lead arsenate in decreasing the concentration of citrate in citrus fruits, with the hope of finding non-toxic acid-reducing chemicals. Solution of 0.3% lead arsenate was sprayed on satsuma mandarin (Citrus unshiu) trees 3 to 7 weeks after full bloom.<br>Free acidity of juice at harvest was 15 to 36% lower in fruits sprayed with lead arsenate than in fruits unsprayed. Lead arsenate sprays did not affect protein content of the pulp. At the stage when juice acidity increased rapidly, CS activity was lower in the sprayed fruits than in the unsprayed ones. An interrelation between the reduction of CS activity and the reduction of free acidity was observed. A correlation between rate of decrease in CS activity by lead arsenate 9 to 12 weeks after full bloom and rate of decrease in free acidity at harvest season was also seen.<br>When lead arsenate was added to measuring cuvettes containing enzyme extract from unsprayed fruits picked in August, CS activity decreased in proportion to the amount of lead arsenate added to the cuvettes.<br>When fruits began to color, CS activity of sprayed fruits exceeded that of unsprayed fruits. The fact that high CS activity at fruit coloring stage did not increase the free acidity of juice may be explained by the changes in metabolism of organic acids.

Effect of Lead Arsenate on Citrate Synthase Activity in Fruit Pulp of Satsuma Mandarin

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