Feyereisen R, Farnsworth D E
Department of Entomology, Oregon State University, Corvallis 97331.
Mol Cell Endocrinol. 1987 Oct;53(3):227-38. doi: 10.1016/0303-7207(87)90178-x.
The enzyme 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase was characterized in cockroach corpora allata which produce insect juvenile hormone III (methyl-(10R)10,11-epoxy-3,7,11-tri-methyl-2E,6E-dodecadienoate ). HMG-CoA reductase is a microsomal enzyme dependent on NADPH and dithiothreitol (or glutathione) for activity. The enzyme selectively reduced (3S)-HMG-CoA to (3R)-mevalonate with an apparent KM of 7.6 microM. Mevinolin was a competitive inhibitor of HMG-CoA reductase with a KI of 2.4 nM. No evidence for a modulation of enzyme activity by phosphorylation was obtained. Levels of HMG-CoA reductase were not altered after incubation of the corpora allata with either mevinolin (to decrease isoprenoid flux) or with mevalonate or farnesol (to increase isoprenoid flux). Split pairs of corpora allata were used to compare JH III synthetic activity with HMG-CoA reductase activity during the cycle of JH III synthesis that controls vitellogenesis and oocyte growth in adult females. Both activities changed over 10-fold and peaked on day 5 after emergence/mating, but JH III synthesis did not parallel HMG-CoA reductase activity precisely thereafter. The half-life of HMG-CoA reductase measured in the presence of cycloheximide was significantly different between low and high activity glands and was not related to the half-life of JH III synthesis. The results suggest that HMG-CoA reductase should not be considered 'the rate-limiting enzyme' in juvenile hormone synthesis by Diploptera punctata corpora allata.
在能产生昆虫保幼激素III（甲基-(10R)10,11-环氧-3,7,11-三甲基-2E,6E-十二碳二烯酸酯）的蟑螂咽侧体中对3-羟基-3-甲基戊二酰辅酶A（HMG-CoA）还原酶进行了特性研究。HMG-CoA还原酶是一种微粒体酶，其活性依赖于NADPH和二硫苏糖醇（或谷胱甘肽）。该酶将(3S)-HMG-CoA选择性还原为(3R)-甲羟戊酸，表观KM为7.6微摩尔。美伐他汀是HMG-CoA还原酶的竞争性抑制剂，KI为2.4纳摩尔。未获得酶活性受磷酸化调节的证据。用美伐他汀（以降低类异戊二烯通量）或甲羟戊酸或法尼醇（以增加类异戊二烯通量）孵育咽侧体后，HMG-CoA还原酶的水平未发生改变。使用分离的成对咽侧体来比较保幼激素III合成活性与HMG-CoA还原酶活性，该合成活性处于控制成年雌性卵黄发生和卵母细胞生长的保幼激素III合成周期中。两种活性均变化超过10倍，并在羽化/交配后第5天达到峰值，但此后保幼激素III合成与HMG-CoA还原酶活性并非精确平行。在存在环己酰亚胺的情况下测定的HMG-CoA还原酶的半衰期在低活性和高活性腺体之间存在显著差异，且与保幼激素III合成的半衰期无关。结果表明，在双点蔗蠊咽侧体合成保幼激素的过程中，HMG-CoA还原酶不应被视为“限速酶”。
