1. A factor, which amplifies the inductions of several liver enzymes by glucocorticoid, was partially purified from Proteus mirabilis from rat intestine. The factor (amplifier) was completely inactivated by ct-glucosidase, but not by other glycoside hydrolases, proteases, nucleases or phosphatases tested; it was also hydrolysed by HCI with liberation of reducing sugars. Thus the oligosaccharide in this factor seems to be essential for the amplification.2. In adrenalectomized rats the amplifier increased the inductions of several liver enzymes, such as tyrosine aminotransferase and leucine aminotransferase, by glucocorticoid. But it did not amplify the induction of tyrosine aminotransferase by glucagon or insulin or the activities of enzymes that are not induced by glucocorticoid. The amplifier by itself did not have any glucocorticoid-like action in adrenalectomized rat. These results show that the amplifier specifically increases the inductions of liver enzymes by glucocorticoid.3. Since a similar amplification was also observed in isolated perfused liver and cultured hepatoma cells in vitro, the amplifier seems to act directly on the target organ or cells.Previously we found that administration of a small dose of glucocorticoid induced less liver tyrosine aminotransferase in germ-free rats than in normal rats. This suggested that intestinal flora increased the action of glucocorticoid.Therefore, we examined the actions of fractions of enteric bacteria on the induction of liver enzymes by glucocorticoid. We isolated a fraction that amplified the inductions of several liver enzymes by glucocorticoid: it had a direct action on the liver or cells in the presence of glucocorticoid, but none in the absence of glucocorticoid. Fractions with amplifying actions were obtained from several enteric bacteria, such as Proteus mirabilis, Laclobacillus and Streptococcus, but not Saccharomyces; the fraction from P. mirahilis had the most activity. The factor purified from P. mirahilis is effective at very low concentration,
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