Urease activity in artificial diet for the silkworm, Bombyx mori, and in mulberry leaves and soybean seeds.

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  • 家蚕の人工飼料ならびに桑葉およびダイズ種子のウレアーゼ活性
  • カサン ノ ジンコウ シリョウ ナラビニ ソウヨウ オヨビ ダイズ シュシ ノ

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Abstract

When reared on artificial diets, silkworms were unable to break down the urea derived from arginine and uric acid in the body due to the lack of urease. Urea consequently accumulated in all pupal organs including feces, urine, cocoon layers and eggs. This abnormal nitrogen metabolism was not observed in silkworms reared on mulberry leaves. The level of urease activity in 6 different preparations of artificial-diet powders was very high. The urease activity in the dietpowder was completely inactivated in the process of final treatment when water was added and the product steamed. Mulberry-leaf powder and soybean are the main raw materials of the artificial diet for silkworms. Fresh mulberry leaves displayed a distinct urease activity, especially the grown leaves sampled from a low position of the mulberry shoot. Urease activity of mulberry leaves varied widely among the varieties, that of the Keguwa variety having the highest value, which was about 6 times that of Shinso which displayed the lowest value. Comparisonn of Urease activity between 4 strains of mulberry varieties showed that M. alba L. and Tropical race exhibited significantly higher activities than M. latifola P. and M. bombycis K.. Furthermore, urease activity in mulberry tree was also detected in the roots and shoots, with an especially high level in root hairs. Urease activity in leaf-powder prepared after freeze-drying and drying at 55°C was 27% and 46% lower than that in fresh leaves, respectively, and drying at 90°C completely destroyed this enzyme activity. Soybean seeds, another major material for the artificial diet, also showed a high urease activity with considerable variations among the soybean varieties; Shiro tsurunoko, a cultured type, exhibited the highest urease activity among 20 varieties, while Miyakojima tsurumame, a wild type, showed the lowest activity.

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