Activation of liver tryptophan oxygenase by hydrocortisone, hematin and tryptophan in streptozotocin-diabetic rats.
This study compared changes in liver tryptophan oxygenase (TPO) activity in response to hydrocortisone, hematin and tryptophan administration to non-diabetic and diabetic (streptozotocin) rats. Hydrocortisone caused similar increases in apoenzyme (inactive), holoenzyme (heme-saturated) and total (holoenzyme + apoenzyme) TPO activities in non-diabetic and diabetic rats. The ability of hematin to increase total TPO activity was significantly less in diabetic rats. The largest differences between diabetic and non-diabetic rats were found with tryptophan which increased total TPO and holoenzyme activities 300% and 650% respectively in non-diabetic rats. However, tryptophan increased both apoenzyme (unchanged in non-diabetic rats) and holoenzyme activities by 300% in diabetic rats. These results indicate that in the diabetic state, the TPO-heme conjugation process is impaired, especially substrate mediated TPO-heme saturation.
D000818:Animals; D001051:Apoenzymes / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D006418:Heme / Q000031:analogs & derivatives*; D006427:Hemin / Q000494:pharmacology*; D006854:Hydrocortisone / Q000494:pharmacology*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014364:Tryptophan / Q000494:pharmacology*; D014366:Tryptophan Oxygenase / Q000378:metabolism*
D001051:Apoenzymes; D006418:Heme; D006427:Hemin; D014364:Tryptophan; D014366:Tryptophan Oxygenase; D006854:Hydrocortisone