Rydell E L, Axelsson K L, Wikberg J E
Acta Pharmacol Toxicol (Copenh). 1985 Mar;56(3):214-20. doi: 10.1111/j.1600-0773.1985.tb01278.x.
The effect of retinylacetate (RA) was investigated on rat liver guanylate cyclase stimulated by nitroprusside (NP). The stimulated enzyme seemed to adhere to Michaëlis-Menten kinetics with an apparent Km for MnGTP of 0.10 mM and a Vmax of 410 pmol cGMP/min. X mg prot. RA (0.1-1mM) dose-dependently inhibited the enzyme stimulated by NP (0.1-10 mM). In the presence of 1 mM RA the activity was only 10% of the control activity. The inhibitory action of RA seemed to be non-competitive since it depressed Vmax without affecting the Km for MnGTP. In contrast, however, RA was instead found to stimulate the enzyme when low concentrations of NP (0.01-0.1 mM) were used. The concentration-activity curve for NP was bell-shaped showing an optimum at 0.5 mM. The inhibition induced by RA could not be surmounted by increasing the NP concentration indicating that RA did not compete with NP. A bell-shaped activity curve was also seen when the enzyme activity was measured in the presence of increasing Mn2+ concentrations and during these conditions RA also caused inhibition. In the presence of the sulphydryl reductant dithiothreitol (DTT), the NP concentration needed for optimal enzyme activation was about 100-fold less than in the absence of DTT. The maximal enzyme activity was also slightly increased. In the presence of DTT, RA was much less effective to induce inhibition of the stimulated enzyme, than when DDT was absent. (In the presence of DTT 1 mM RA caused only 30% inhibition compared to 90% inhibition in its absence).(ABSTRACT TRUNCATED AT 250 WORDS)
研究了醋酸视黄酯（RA）对硝普钠（NP）刺激的大鼠肝脏鸟苷酸环化酶的作用。受刺激的酶似乎符合米氏动力学，对MnGTP的表观Km为0.10 mM，Vmax为410 pmol cGMP/分钟。X毫克蛋白。RA（0.1 - 1 mM）剂量依赖性地抑制NP（0.1 - 10 mM）刺激的酶。在1 mM RA存在下，活性仅为对照活性的10%。RA的抑制作用似乎是非竞争性的，因为它降低了Vmax而不影响对MnGTP的Km。然而，相反的是，当使用低浓度的NP（0.01 - 0.1 mM）时，发现RA反而刺激该酶。NP的浓度 - 活性曲线呈钟形，在0.5 mM时显示最佳值。RA诱导的抑制不能通过增加NP浓度来克服，表明RA不与NP竞争。当在增加的Mn2 +浓度存在下测量酶活性时，也观察到钟形活性曲线，在这些条件下RA也引起抑制。在巯基还原剂二硫苏糖醇（DTT）存在下，最佳酶激活所需的NP浓度比不存在DTT时少约100倍。最大酶活性也略有增加。在DTT存在下，RA诱导对受刺激酶的抑制作用比不存在DTT时要小得多。（在存在DTT的情况下，1 mM RA仅引起30%的抑制，而在不存在DTT时为90%的抑制）。（摘要截断于250字）
