Holm I, Persson L, Pegg A E, Heby O
Department of Zoophysiology, University of Lund, Sweden.
Biochem J. 1989 Jul 1;261(1):205-10. doi: 10.1042/bj2610205.
The rate-limiting enzymes in polyamine biosynthesis, ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC), are negatively regulated by the polyamines spermidine and spermine. In the present work the spermidine synthase inhibitor S-adenosyl-1,8-diamino-3-thio-octane (AdoDATO) and the spermine synthase inhibitor S-methyl-5'-methylthioadenosine (MMTA) were used to evaluate the regulatory role of the individual polyamines. Treatment of Ehrlich ascites-tumour cells with AdoDATO caused a marked decrease in spermidine content together with an accumulation of putrescine and spermine. Treatment with MMTA, on the other hand, gave rise to a marked decrease in spermine, with a simultaneous accumulation of spermidine. A dramatic increase in the activity of AdoMetDC, but not of ODC, was observed in MMTA-treated cells. This increase appears to be unrelated to the decrease in spermine content, because a similar rise in AdoMetDC activity was obtained when AdoDATO was given in addition to MMTA, in which case the spermine content remained largely unchanged. Instead, we show that the increase in AdoMetDC activity is mainly due to stabilization of the enzyme, probably by binding of MMTA. Treatment with AdoDATO had no effects on the activities of ODC and AdoMetDC, even though it caused a precipitous decrease in spermidine content. The expected decrease in spermidine-mediated suppression of ODC and AdoMetDC was most probably counteracted by the simultaneous increase in spermine. The combination of AdoDATO and MMTA caused a transient rise in ODC activity. Concomitant with this rise, the putrescine and spermidine contents increased, whereas that of spermine remained virtually unchanged. The increase in ODC activity was due to increased synthesis of the enzyme. There were no major effects on the amount of AdoMetDC mRNA by treatment with the inhibitors, alone or in combination. However, the synthesis of AdoMetDC was slightly stimulated in cells treated with MMTA or AdoDATO plus MMTA. The present study demonstrates that regulation of neither ODC nor AdoMetDC is a direct function of the polyamine structure. Instead, it appears that the biosynthesis of the polyamines is feedback-regulated by the various polyamines at many different levels.
多胺生物合成中的限速酶，即鸟氨酸脱羧酶（ODC）和S-腺苷甲硫氨酸脱羧酶（AdoMetDC），受到多胺亚精胺和精胺的负调控。在本研究中，使用亚精胺合酶抑制剂S-腺苷-1,8-二氨基-3-硫代辛烷（AdoDATO）和精胺合酶抑制剂S-甲基-5'-甲硫基腺苷（MMTA）来评估单个多胺的调节作用。用AdoDATO处理艾氏腹水瘤细胞会导致亚精胺含量显著降低，同时腐胺和精胺积累。另一方面，用MMTA处理会导致精胺显著减少，同时亚精胺积累。在MMTA处理的细胞中观察到AdoMetDC活性显著增加，但ODC活性未增加。这种增加似乎与精胺含量的降低无关，因为当除了MMTA之外还给予AdoDATO时，AdoMetDC活性也有类似的升高，在这种情况下精胺含量基本保持不变。相反，我们表明AdoMetDC活性的增加主要是由于酶的稳定，可能是通过MMTA的结合。用AdoDATO处理对ODC和AdoMetDC的活性没有影响，尽管它导致亚精胺含量急剧下降。亚精胺介导的对ODC和AdoMetDC的抑制作用预期的降低很可能被同时增加的精胺抵消。AdoDATO和MMTA的组合导致ODC活性短暂升高。伴随着这种升高，腐胺和亚精胺含量增加，而精胺含量基本保持不变。ODC活性的增加是由于酶的合成增加。单独或联合使用抑制剂处理对AdoMetDC mRNA的量没有主要影响。然而，在MMTA或AdoDATO加MMTA处理的细胞中，AdoMetDC的合成受到轻微刺激。本研究表明，ODC和AdoMetDC的调节都不是多胺结构的直接功能。相反，似乎多胺的生物合成在许多不同水平上受到各种多胺的反馈调节。
