A graphene oxide-based covalent resorufin-conjugated fluorescence "off-on" probe for detection of hydrazine

The unique properties of graphene oxide (GO), such as good water solubility, non-toxicity, biocompatibility and cell permeability, make GO well suited for a number of biological applications. In this study, we explore the application of GO as an efficient fluorescent quencher for a highly fluorescent organic dye, resorufin (RF). The quenching effect of GO on resorufin is studied by noncovalent and covalent bonding of resorufin, respectively. The fluorescence is completely quenched when resorufin is covalently linked to GO; while resorufin's fluorescence could be still observed through noncovalent bonding to GO sheet. Interestingly, addition of hydrazine into RF-GO complex causes the fluorescence recovered, providing a potential ''OFF-ON'' fluorescence responsive probe for detecting hydrazine in vitro and in living cells.

Multiplexing fluorogenic esterase-based viability assay with luciferase assays

Luciferase-based reporter assays are one of the most common cell-based screening formats for drug discovery, and simultaneous evaluation of the cytotoxic effect of test compounds is of great value in reducing false-positives. Here we share a multiplex assay protocol that allows sequential measurement of cell viability (cell number) and luciferase activity of the same sample in a multi-well-plate format. The viability assay employs a fluorogenic esterase substrate, CytoRed.

•

This protocol allows sequential measurement of endogenous esterase activity (as a surrogate for cell number) and then luciferase activity in a single sample.

•

The protocol eliminates the need for parallel viability assay or protein assay using separate aliquots of the lysate.

•

This protocol is especially useful for assays with cells stably expressing a luciferase construct, for which co-transfection of another reporter gene is not a viable option.

Recent developments in the localization of oil body-associated signaling molecules during lipolysis in oilseeds

Prior to and/or accompanying lipolytic degradation of triacylglycerols (TAGs) during seed germination in oilseeds, certain enzymatic and non-enzymatic signaling molecules are expressed on the oil body membranes. These include certain proteases, lipoxygenase, phospholipase A(2) and lipase. Although enough biochemical investigations have demonstrated their activities, recent developments in the in situ localization of these signaling molecules in germinating oilseeds, have enhanced our understanding in this field. This is evident from the temporal and spatial changes observed in the expression pattern of some of these molecules. Present review aims at providing an up-to-date account of these recent developments in the author's and other laboratories, which are largely based on fluorescence microscopic and confocal laser scanning microscopic (CLSM) imaging of the molecular changes using specific fluorescent probes. A model for the molecular events associated with oil body mobilization is also being presented.

Human NAD(P)H:quinone oxidoreductase inhibition by flavonoids in living cells

Procedures for assessing enzyme inhibition in living cells are an important tool in the study of the relevance of enzyme-catalyzed reactions and interactions in the human body. This paper presents the effects of flavonoids on NAD(P)H:quinone oxidoreductase 1 (NQO1) activity, by a newly developed method to measure NQO1 inhibition in intact cells. The principle of this method is based on the resorufin reductase activity of NQO1. The change in fluorescence in time was used to determine NQO1 activity in intact Chinese hamster ovary (CHO) cells genetically engineered to overexpress human NQO1. Applying this method to determine the inhibitory effects of reported in vitro NQO1 inhibitors (dicoumarol, 7,8-dihydroxyflavone, chrysin) showed that for all inhibitors tested, the IC50 in intact cells was at least 3 orders of magnitude higher than the IC50 in cell lysates. This result demonstrates that in vitro studies with purified NQO1 or with extracts from disrupted tissues are of limited value for obtaining insight into the situation in living cells. Possible factors underlying this discrepancy are being discussed. For the first time, we determined NQO1 inhibition by flavonoids in cells without disruption of the cells or addition of cofactors, enabling the assessment of enzymatic activity and the interaction of modulators of enzymatic activity in an intracellular situation.