Rosenberg G B, Pall M L
Arch Biochem Biophys. 1983 Feb 15;221(1):243-53. doi: 10.1016/0003-9861(83)90141-8.
A novel adenylate cyclase activity was found in crude homogenates of Neurospora crassa. The adenylate cyclase had substantial activity with ATP-Mg2+ as substrate differing significantly from the strictly ATP-Mn2+-dependent enzyme characterized previously. Additionally, the ATP-Mg2+-dependent activity was stimulated two- to fourfold by GTP or guanyl-5'-yl-imido-diphosphate (Gpp(NH)p). We propose that the ATP-Mg2+-dependent, guanine nucleotide-stimulated activity is due to a labile regulatory component (G component) of the adenylate cyclase which was present in carefully prepared extracts. The adenylate cyclase had a pH optimum of 5.8 and both the catalytic and G component were particulate. The Km for ATP-Mg2+ was 2.2 mM in the presence of 4.5 mM excess Mg2+. Low Mn2+ concentrations had no effect on adenylate cyclase activity whereas high concentrations of Mn2+ or Mg2+ stimulated the enzyme. Maximal Gpp(NH)p stimulation required preincubation of the enzyme in the presence of the guanine nucleotide and the K1/2 for Gpp(NH)p stimulation was 110 nM. Neither fluoride nor any of a variety of glycolytic intermediates or hormones, including glucagon, epinephrine, and dopamine, had an effect on ATP-Mg2+-dependent adenylate cyclase activity. However, the enzymatic activity was stimulated not only by GTP but also by 5'-AMP and was inhibited by NADH.
在粗糙脉孢菌的粗匀浆中发现了一种新型腺苷酸环化酶活性。该腺苷酸环化酶以ATP-Mg2+作为底物时具有较高活性，这与之前所描述的严格依赖ATP-Mn2+的酶有显著差异。此外，GTP或鸟苷-5'-基-亚氨基二磷酸（Gpp(NH)p）可使依赖ATP-Mg2+的活性提高两到四倍。我们推测，依赖ATP-Mg2+且受鸟嘌呤核苷酸刺激的活性是由于腺苷酸环化酶中一种不稳定的调节成分（G成分）所致，该成分存在于精心制备的提取物中。该腺苷酸环化酶的最适pH为5.8，催化成分和G成分均为颗粒状。在存在4.5 mM过量Mg2+的情况下，ATP-Mg2+的Km为2.2 mM。低浓度的Mn2+对腺苷酸环化酶活性无影响，而高浓度的Mn2+或Mg2+则刺激该酶。Gpp(NH)p的最大刺激作用需要在鸟嘌呤核苷酸存在下对酶进行预孵育，Gpp(NH)p刺激的K1/2为110 nM。氟化物以及包括胰高血糖素、肾上腺素和多巴胺在内的多种糖酵解中间产物或激素，均对依赖ATP-Mg2+的腺苷酸环化酶活性无影响。然而，该酶活性不仅受到GTP的刺激，还受到5'-AMP的刺激，并被NADH抑制。
