No abstract

Type-2 isopentenyl diphosphate isomerase, which catalyzes the interconversion if isopentenyl diphosphate and dimethylallyl diphosphate, contains a tightly bound molecule of FMN. Incubation of the active enzyme•FMNH 2 complex with an analog of isopentenyl diphosphate, where the methyl group has been replaced with a cyclopropane ring, results in isomerization of the analog to the corresponding allylic isomer without inactivation of the enzyme. In contrast, the related epoxide analog is a potent irreversible inhibitor that covalently modifies the flavin cofactor in a protoninitiated reaction. These results suggest that the mechanism for isomerization by the type-2 isopentenyl diphosphate isomerase may be similar to the protonation-deprotonation sequence of the type-1 enzyme and places limits on the lifetimes of radical intermediates in an alternative hydrogen atom addition/abstraction mechanism. Publisher's Disclaimer: This PDF receipt will only be used as the basis for generating PubMed Central (PMC) documents. PMC documents will be made available for review after conversion (approx. 2-3 weeks time). Any corrections that need to be made will be done at that time. No materials will be released to PMC without the approval of an author.

The direct reaction of alkali metals with certain aromatic hydrocarbons has been reported previously in the literature, the reaction of sodium with anthracene in ethyl ether solution1 being an example. Efforts to extend this reaction to simpler hydrocarbons such as naphthalene and diphenyl have met with very limited success. Schlenk and Bergmann were able to cause lithium to react with these hydrocarbons to a sufficient extent to make some examination of the products2 but reported no detectable reaction with sodium under similar conditions.

Animal models recapitulating COVID-19 are critical to enhance our understanding of SARS-CoV-2 pathogenesis. Intranasally inoculated transgenic mice expressing human angiotensin-converting enzyme 2 under the cytokeratin 18 promoter (K18-hACE2) represent a lethal model of SARS-CoV-2 infection. We evaluated the clinical and virological dynamics of SARS-CoV-2 using two intranasal doses (104 and 106 PFUs), with a detailed spatiotemporal pathologic analysis of the 106 dose cohort. Despite generally mild-to-moderate pneumonia, clinical decline resulting in euthanasia or death was commonly associated with hypothermia and viral neurodissemination independent of inoculation dose. Neuroinvasion was first observed at 4 days post-infection, initially restricted to the olfactory bulb suggesting axonal transport via the olfactory neuroepithelium as the earliest portal of entry. Absence of viremia suggests neuroinvasion occurs independently of transport across the blood-brain barrier. SARS-CoV-2 tropism was neither restricted to ACE2-expressing cells (e.g., AT1 pneumocytes), nor inclusive of some ACE2-positive cell lineages (e.g., bronchiolar epithelium and brain vasculature). Absence of detectable ACE2 protein expression in neurons but overexpression in neuroepithelium suggest this as the most likely portal of neuroinvasion, with subsequent ACE2 independent lethal neurodissemination. A paucity of epidemiological data and contradicting evidence for neuroinvasion and neurodissemination in humans call into question the translational relevance of this model.

Isopentenyl diphosphate isomerase (IDI) catalyzes the interconversion of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), the basic building blocks of isoprenoid molecules. Two structurally unrelated classes of IDI are known. Type I IPP isomerase (IDI-1) utilizes a divalent metal in a protonation-deprotonation reaction; whereas, the type II enzyme (IDI-2) requires reduced flavin. Epoxy, diene, and fluorinated substrate analogues, irreversible inhibitors of IDI-1, were analyzed as mechanistic probes for IDI-2. 3,4-Oxido-3-methyl-1-butyl diphosphate (eIPP), 3-methylene-4-penten-1-yl diphosphate (vIPP), and 3-(fluoromethyl)-3-buten-1-yl diphosphate (fmIPP) inactivate IDI-2 through formation of covalent adducts with the reduced flavin. UV-visible spectra of the inactivated complexes are consistent with modification of the isoalloxazine ring at position N5. vIPP and fmIPP are also alternate substrates with isomerization competing with alkylation of the flavin cofactor. (Z)-3-(Fluoromethyl)-2-buten-1-yl diphosphate ((Z)-fmDMAPP) and (Z)-3-(difluoromethyl)-2-buten-1-yl diphosphate ((Z)-dfmDMAPP) are alternate substrates, which are isomerized to the corresponding IPP derivatives. The rates of isomerization of fmIPP and (Z)-fmDMAPP are approximately 50-fold less than IPP and DMAPP, respectively. dfmIPP is not an irreversible inhibitor. These studies indicate that the irreversible inhibitors inactivate the reduced flavin required for catalysis by electrophilic alkylation and are consistent with a protonation-deprotonation mechanism for the isomerization catalyzed by IDI-2.