3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Activity in Ochromonas malhamensis

Abstract

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the key regulatory enzyme of the isoprenoid pathway, was found to be predominantly microsomal in Ochromonas malhamensis, a chrysophytic alga. Detection of HMG-CoA reductase requires the presence of 1% bovine serum albumin during cell homogenization, and the activity is stimulated by the presence of Triton X-100. The enzyme has a pH optimum of 8.0 and an absolute requirement for NADPH. When grown in 10 micromolar mevinolin, a competitive inhibitor of HMG-CoA reductase, 0. malhamensis shows a 10-to 15-fold increase in HMG-CoA reductase activity (after washing) with little or no effect on cell growth rate. Cultures can be maintained in 10 micromolar mevinolin for months. 0. malhamensis produces a large amount (1% dry weight) of poriferasterol, a product of the isoprenoid pathway. The addition of 10 micromolar mevinolin initially blocked poriferasterol biosynthesis by >90%; within 2 days the rate of synthesis returned to normal levels. Immediately after mevinolin was washed from the 2-day culture, there was a transient 2.5-fold increase in the rate of poriferasterol biosynthesis. The rate of poriferasterol biosynthesis and the level of HMG-CoA reductase activity both fell to control levels within hours.

Mevalonosomes: specific vacuoles containing the mevalonate pathway in Plocamium brasiliense cortical cells (Rhodophyta)

“…Maurey et al. () determined that HGMR activity exists in the microssomal fraction of the alga Ochromonas malhamensis (Chrysophyta). In addition, vesicles enriched with HMGR were found in Arabidopsis cells, possibly representing the basis of isoprenoid biosynthesis in this species (Enjuto et al.…”

“…There is evidence that the mevalonate pathway, or some of its component steps, may be compartmentalized in vesicles or vacuoles (Nagegowda 2010). Maurey et al (1986) determined that HGMR activity exists in the microssomal fraction of the alga Ochromonas malhamensis (Chrysophyta). In addition, vesicles enriched with HMGR were found in Arabidopsis cells, possibly representing the basis of isoprenoid biosynthesis in this species (Enjuto et al 1994).…”

Cloning and characterization of the gene encoding 3-hydroxy-3-methylglutaryl coenzyme A reductase in melon (Cucumis melo L. reticulatus)

“…HMGR catalyzes the conversion of HMG-CoA into mevalonate (MVA), which is the precursor of phytosterols (Gillaspy et al 1993). Since HMGR is an important control point for the mevalonate pathway in plants (Maurey et al 1986), the increase in HMGR should result in increasing the supply of phytosterol. In addition, sterols are major components of the eukaryotic cell membrane, and are required for the production of cell membrane, which is a necessary step in cell division.…”

Characterization and Function of 3-Hydroxy-3-Methylglutaryl-CoA Reductase in Populus trichocarpa: Overexpression of PtHMGR Enhances Terpenoids in Transgenic Poplar

“…The synthesis of IPP and its allylic isomer DMAPP is the first step in both the MVA and MEP pathways. 3-Hydroxy-3-methylglutaryl-CoA reductase (HMGR) catalyzes the conversion of one molecule of 3-hydroxy-3-methylglutary-CoA (HMG-CoA) and two molecules of triphosphopyridine nucleotide (NADPH) into MVA (Maurey et al, 1986). Because HMGR activity is highly regulated, HMGR is considered the rate-limiting enzyme in the upstream biosynthetic pathway of hemiterpenes and triterpenes (Heuston et al, 2012).…”