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Liu W.,University of Miami | Johnson S.,University of Miami | Micic M.,MP Biomedicals LLC | Micic M.,University of California at Irvine | And 4 more authors.
Langmuir | Year: 2012

The human insulin (HI) Langmuir monolayer at the air-water interface was systematically investigated in the presence and absence of Zn(II) ions in the subphase. HI samples were dissolved in acidic (pH 2) and basic (pH 9) aqueous solutions and then spread at the air-water interface. Spectroscopic data of aqueous solutions of HI show a difference in HI conformation at different pH values. Moreover, the dynamics of the insulin protein showed a dependence on the concentration of Zn(II) ions. In the absence of Zn(II) ions in the subphase, the acidic and basic solutions showed similar behavior at the air-water interface. In the presence of Zn(II) ions in the subphase, the surface pressure-area and surface potential-area isotherms suggest that HI may aggregate at the air-water interface. It was observed that increasing the concentration of Zn(II) ions in the acidic (pH 2) aqueous solution of HI led to an increase of the area at a specific surface pressure. It was also seen that the conformation of HI in the basic (pH 9) medium had a reverse effect (decrease in the surface area) with the increase of the concentration of Zn(II) ions in solution. From the compression-decompression cycles we can conclude that the aggregated HI film at air-water interface is not stable and tends to restore a monolayer of monomers. These results were confirmed from UV-vis and fluorescence spectroscopy analysis. Infrared reflection-absorption and circular dichroism spectroscopy techniques were used to determine the secondary structure and orientation changes of HI by zinc ions. Generally, the aggregation process leads to a conformation change from ?-helix to β-strand and β-turn, and at the air-water interface, the aggregation process was likewise seen to induce specific orientations for HI in the acidic and basic media. A proposed surface orientation model is presented here as an explanation to the experimental data, shedding light for further research on the behavior of insulin as a Langmuir monolayer. © 2012 American Chemical Society. Source


Thakur G.,University of Miami | Pao C.,University of Miami | Micic M.,MP Biomedicals LLC | Micic M.,University of California at Irvine | And 2 more authors.
Colloids and Surfaces B: Biointerfaces | Year: 2011

Lipid rafts being rich in cholesterol and sphingolipids are considered to provide ordered lipid environment in the neuronal membranes, where it is hypothesized that the cleavage of amyloid precursor protein (APP) to Aβ (1-40) and Aβ (1-42) takes place. It is highly likely that the interaction of lipid raft components like cholesterol, sphingomylein or GM1 leads to nucleation of Aβ and results in aggregation or accumulation of amyloid plaques. One has investigated surface pressure-area isotherms of the lipid raft and Aβ (1-40) Langmuir monolayer. The compression-decompression cycles and the stability of the lipid raft Langmuir monolayer are crucial parameters for the investigation of interaction of Aβ (1-40) with the lipid raft Langmuir monolayer. It was revealed that GM1 provides instability to the lipid raft Langmuir monolayer. Adsorption of Aβ (1-40) onto the lipid raft Langmuir monolayer containing neutral (POPC) or negatively charged phospholipid (DPPG) was examined. The adsorption isotherms revealed that the concentration of cholesterol was important for adsorption of Aβ (1-40) onto the lipid raft Langmuir monolayer containing POPC whereas for the lipid raft Langmuir monolayer containing DPPG:cholesterol or GM1 did not play any role. In situ UV-vis absorption spectroscopy supported the interpretation of results for the adsorption isotherms. © 2011 Elsevier B.V. Source


Thakur G.,University of Miami | Micic M.,MP Biomedicals LLC | Micic M.,University of California at Irvine | Leblanc R.M.,University of Miami
Journal of Physical Chemistry C | Year: 2010

Nanoparticle chemistry is emerging in the field of nanomedicine and nanodiagnostics. In recent times quantum dots have been considered as potential probes for bioimaging. These particles can be beneficial when it comes to study neurodegenerative diseases such as Alzheimer's disease. Amyloid beta (1-42) (Aβ (1-42)) is a polypeptide that is the major constituent of the plaques in Alzheimer's disease patients. We have examined the surface and spectroscopic properties of Aβ (1-42) mixed with or conjugated to dihydrolipoic acid- and poly(ethylene glycol)-capped CdSe/ZnS quantum dots. Surface pressure-area isotherms and in situ UV-vis absorption and fluorescence spectroscopy were used to characterize the Aβ (1-42) mixed with or conjugated to quantum dots at the air-water interface. The capping of quantum dots played a role in surface chemistry as was determined by surface pressure-area isotherms and spectroscopic properties of the Langmuir monolayer. © 2010 American Chemical Society. Source


Boggess M.V.,U.S. Department of Agriculture | Lippolis J.D.,U.S. Department of Agriculture | Hurkman W.J.,U.S. Department of Agriculture | Fagerquist C.K.,U.S. Department of Agriculture | And 5 more authors.
Journal of Proteomics | Year: 2013

Increase in the world population has called for the increased demand for agricultural productivity. Traditional methods to augment crop and animal production are facing exacerbating pressures in keeping up with population growth. This challenge has in turn led to the transformational change in the use of biotechnology tools to meet increased productivity for both plant and animal systems. Although many challenges exist, the use of proteomic techniques to understand agricultural problems is steadily increasing. This review discusses the impact of genomics, proteomics, metabolomics and phenotypes on plant, animal and bacterial systems to achieve global food security and safety and we highlight examples of intra and extra mural research work that is currently being done to increase agricultural productivity. Biological significance: This review focuses on the global demand for increased agricultural productivity arising from population growth and how we can address this challenge using biotechnology. With a population well above seven billion humans, in a very unbalanced nutritional state (20% overweight, 20% risking starvation) drastic measures have to be taken at the political, infrastructure and scientific levels. While we cannot influence politics, it is our duty as scientists to see what can be done to feed humanity. Hence we highlight the transformational change in the use of biotechnology tools over traditional methods to increase agricultural productivity (plant and animal). Specifically, this review deals at length on how a three-pronged attack, namely combined genomics, proteomics and metabolomics, can help to ensure global food security and safety.This article is part of a Special Issue entitled: Translational Plant Proteomics. © 2013 Elsevier B.V. Source


Orbulescu J.,University of Miami | Micic M.,MP Biomedicals LLC | Micic M.,University of California at Irvine | Ensor M.,University of Kentucky | And 3 more authors.
Langmuir | Year: 2010

Human cardiac troponin I (cTnI) is the preferred biomarker in the assessment of myocardial infarction. It is known to interact with troponin C and T to form a trimeric complex. Whereas small amounts are found in the cytoplasm, most of cTnI is in the form of a complex with actin located in myofilaments. To understand these interactions of cTnI better, we first investigated the surface chemistry of cTnI as a Langmuir monolayer spread at the air-water interface. We investigated the optimal conditions for obtaining a stable Langmuir monolayer in terms of changing the ionic strength of the subphase using different concentrations of potassium chloride. Monolayer stability was investigated by compressing the cTnI monolayer to a specific surface pressure and keeping the surface pressure constant while measuring the decrease in the molecular area as a function of time. Aggregation and/or domain formation was investigated by using compression-decompression cycles, in situ UV-vis spectroscopy, Brewster angle microscopy (BAM), and epifluorescence microscopy. To ensure that the secondary structure is maintained, we used infrared reflection-absorption spectroscopy (IRRAS) directly at the air-subphase interface. It was found that cTnI forms a very stable monolayer (after more that 5000 s) that does not aggregate at the air-subphase interface. The cTnI molecules maintain their secondary structure and, on the basis of the low reflectivity observed, using BAM measurements and the low reflection-absorption intensities measured with IRRAS spectroscopy, lie flat on the subphase with the α-helices parallel to the air-subphase interface. © 2009 American Chemical Society. Source

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