|Budget Amount *help
¥2,300,000 (Direct Cost : ¥2,300,000)
Fiscal Year 1991 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1990 : ¥800,000 (Direct Cost : ¥800,000)
Fiscal Year 1989 : ¥800,000 (Direct Cost : ¥800,000)
The activity of ornithine decarboxylase(ODC), which catalyzes the ratelimiting step in the biosynthetic pathway of polyamines, is known to have an extreme short half-life and to show rapid and dramatic stimulation in response to a variety of chemical and physiological stimuli, and therefore its regulatory mechanism is of particular interest. Changes in the ODC activity in the cell should occur as a result of either quantitative changes in the ODC protein or qualitative changes in the enzyme activity, or both. Most works on the regulatory mechanism for ODC activity has so far focused on quantitative changes in ODC protein, especially changes in the rates of ODC mRNA translation and ODC protein degradation. However, the extremely rapid and intense changes in ODC activity in the stimulated cells suggested to me the importance of the enzyme activation/inactivation mechanism in the ODC regulation, and led me to study biological substances affecting ODC activity. Before starting this projec
t, I reported that polyanions such as heparin and anionic phospholipids such as phosphatidylinositol and phosphatidylserine show inhibitory effects, but noncharged phospholipids such as phosphatidylcholine and phoshatidylethanolamine show stimulatory effects on ODC activity. Antizyme, a protein inhibitor specific for ODC, was purified about 600, 000fold to homogeneity from rat liver and its properties were examined. The fact that equilibrium constant of the reaction between antizyme and ODC is as high as 1.4 x 10^<11> M^<-1> indicates the physiological importance of antizyme in the regulation of ODC.
In the present studies, antizyme inhibitor, a protein specifically inhibiting the action of antizyme, was purified about 17, 000, 000-fold from rat liver using antizyme affinity chromatography, and its properties were studied. The results indicate the possible involvement of antizyme/antizyme inhibitor system in the regulation of ODC by posttranslational modification. Renal ODC activity is known to increase by treatment of testosterone. Testosterone induced a 6-fold increase in ODC activity in the mouse kidney, but no significant immunohistochemical difference was observed between the mice with and without testosterone treatment, suggesting that the testosterone-induced increase in the renal ODC activity might not result from increase in the enzyme protein but increase in the enzyme activity. Thus, not only the transcriptional and translational modifications but also the posttranslational modification of ODC appears to play important roles in the regulation of ODC activity in the cell. Less