Purification and characterization of hexahistidine-tagged cyclohexanone monooxygenase expressed in Saccharomyces cerevisiae and Escherichia coli

Cyclohexanone monooxygenase (CMO) is a soluble flavoenzyme originally isolated from Acinetobacter spp. which carries out Baeyer-Villiger reactions with cyclic ketone substrates. In the present study we cloned the Acinetobacter CMO gene and modified it for facile purification from heterologous expression systems by incorporation of a His(6)-tag at its C-terminus. A single purification step employing metal (Ni(2+))-affinity column chromatography provided essentially homogeneous enzyme in yields of 69-72%. The properties of the purified, recombinant enzymes (rCMO) were compared with that of native CMO (nCMO) isolated from Acinetobacter cultures grown in the presence of cyclohexanone. The specific activities of His(6)-tagged rCMO and nCMO toward their index substrate, cyclohexanone, were similar and ranged from 14 to 20 micromol/min/mg. nCMO and rCMO from the Escherichia coli expression system exhibited molecular masses, determined by electrospray mass spectrometry, of 60,800 and 61,615 Da, respectively, an increase for the recombinant enzyme equivalent to the mass of the His(6)-tag. However, rCMO expressed in Saccharomyces cerevisiae consistently exhibited a mass some 50 Da larger than rCMO expressed in bacteria. Edman degradation confirmed that rCMO purified from the E. coli system and nCMO shared the same N-terminal sequence, whereas no sequence information could be obtained for rCMO expressed in yeast. Therefore, the yeast-expressed enzyme possesses an additional posttranslational modification(s), possibly acylation, at the N-terminus. Expression in E. coli is the preferred system for future site-directed mutagenesis studies and crystallization efforts.     

Polyoxygenated cyclohexene derivatives from Ellipeiopsis cherrevensis

Aerial parts of Ellipeiopsis cherrevensis contained the polyoxygenated cyclohexenes zeylenol, ferrudiol and three analogs, ellipeiopsols A, B and C. The C-1 stereochemistry of ferrudiol has been revised.     

Further halotyrosine derivatives from the marine sponge Suberea aff. praetensa

Reexamination of the marine sponge Suberea aff. praetensa, (Row) from the Gulf of Thailand furnished in addition to bromotyrosine derivatives found previously 5-bromo- and 5-chlorocavernicolin, cavernicolins 1 and 2, two other brominated tyrosine metabolites, a known bisoxazolidone and a new unusual rearranged tyrosine metabolite subereatensin. Several of the metabolites exhibited significant inhibitory effects against five human cancer cell lines.     

CDP840. A prototype of a novel class of orally active anti-inflammatory phosphodiesterase 4 inhibitors

The discovery, synthesis and biological activity of a series of triarylethane phosphodiesterase 4 inhibitors is described. Structure-activity relationship studies are presented for CDP840 (29), a potent, chiral, selective inhibitor of PDE 4 (IC(50) 4nM). CDP840 is non-emetic in the ferret at 30mgkg(-1) (po), active in models of inflammation and reverses ozone-induced bronchial hyperreactivity in the guinea pig.     

Interactions of copper with glycated proteins: possible involvement in the etiology of diabetic neuropathy

Humans and animals with diabetes frequently develop peripheral vascular dysfunction and peripheral neuropathies. There is accumulating evidence that impaired peripheral nerve function may derive from diminished endoneural blood flow. The decrements in nerve blood flow may, in turn, be due to diminished endothelium-dependent vasodilation. Although a number of possible causes of this defective vasodilation have been suggested, none has been definitely proven. Regardless of the precise cause, the impaired vasodilatory activity may reflect diminished availability of endothelium-derived relaxing factor (EDRF), variously thought to be nitric oxide or thiol adducts of nitric oxide. Other investigators have reported that administration of transition metal chelators to diabetic rats corrects EDRF-mediated arterial relaxation and restores both neural blood flow and nerve conduction velocity, suggesting the involvement of transition metals. Our investigations center about the hypothesis that glycated proteins bind transition metals such as copper and iron, and that such 'glycochelates' accumulate within the vasculature in diabetes and catalytically inactivate EDRF. In partial support of this hypothesis: (1) Glycated albumin binds approximately 3-fold greater amounts of both copper and iron. (2) Copper bound to glycated albumin remains redox active (e.g. capable of supporting the oxidation of ascorbic acid). (3) Copper and copper-containing glycochelates cause the rapid decomposition of one putative form of EDRF, nitrosocysteine. (4) The amount of exchangeable (i.e. chelatable) copper in the plasma of diabetic rats is approximately twice that in normal rat plasma. (5) Similarly, tail tendons of diabetic animals have about twice as much bound copper as do tendons of normal rats. (6) Implants bearing adsorbed glycated albumin placed in the peritonea of normal mice for 48 h accumulate approximately 5 times as much bound copper as do implants coated with control albumin. Overall, these observations support--but do not conclusively prove - the hypothesis that transition metals such as copper, bound to glycated proteins, may blunt normal EDRF-dependent relaxation of diabetic arteries and provide a rationale for the use of transition metal chelators in the therapy of diabetic vasculopathy and neuropathy.