ABSTRACT
Hydroxyapatite nanocrystals in natural form are a major component of bone--a known piezoelectric material. Synthetic hydroxyapatite is widely used in bone grafts and prosthetic pyroelectric coatings as it binds strongly with natural bone. Nanocrystalline synthetic hydroxyapatite films have recently been found to exhibit strong piezoelectricity and pyroelectricity. While a spontaneous polarization in hydroxyapatite has been predicted since 2005, the reversibility of this polarization (i.e. ferroelectricity) requires experimental evidence. Here we use piezoresponse force microscopy to demonstrate that nanocrystalline hydroxyapatite indeed exhibits ferroelectricity: a reversal of polarization under an electrical field. This finding will strengthen investigations on the role of electrical polarization in biomineralization and bone-density related diseases. As hydroxyapatite is one of the most common biocompatible materials, our findings will also stimulate systematic exploration of lead and rare-metal free ferroelectric devices for potential applications in areas as diverse as in vivo and ex vivo energy harvesting, biosensing and electronics.
Subject(s)
Durapatite/chemistry , Electricity , Nanoparticles/chemistry , Silicon/chemistry , Microscopy, Atomic ForceABSTRACT
Intracellular vesicular trafficking is regulated by Rab proteins, small GTPases that require posttranslational geranylgeranylation for biological activity. This covalent modification is catalyzed by Rab geranylgeranyl transferase (RabGGTase) and proceeds only in the presence of accessory Rab Escort Protein (REP). In this communication, we report the cloning and characterization of REP gene of Arabidopsis thaliana. Highest expression of REP mRNA was detected in leaves and flowers in contrast to stems and roots. AtREP is recognized by anti-rat REP1 serum. Interaction of AtREP with the protein substrate is presented, as well as a structural model obtained through homology modeling, based on the known structure of rat REP1.
Subject(s)
Adaptor Proteins, Signal Transducing/chemistry , Adaptor Proteins, Signal Transducing/isolation & purification , Arabidopsis Proteins/chemistry , Arabidopsis Proteins/isolation & purification , Arabidopsis/chemistry , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/isolation & purification , Amino Acid Sequence , Animals , Cloning, Molecular , Crystallography, X-Ray , Escherichia coli , Flowers/chemistry , Humans , Mice , Models, Molecular , Plant Leaves/chemistry , Protein Conformation , Protein Structure, Tertiary , Rats , Saccharomyces cerevisiae , Sequence Homology, Amino AcidABSTRACT
The influence of physical effort of variable intensity on glycaemia in children was analyzed in 61 children (29 girls and 32 boys) from 5-17 years of age with newly diagnosed diabetes and with diabetes lasting from 1-12 years (5.5 on average) was assessed. The children underwent an exercise test on a thread null. The pulse rate was on indicator of effort. Pulse rate before and after the effort was measured using a Sport-Tester apparatus and the level of glucose in the capillary bloodstream was determined using an Ames glucometer. Three tests of increasing intensity were performed, each lasting 20 minutes on three consecutive days. In children with well controlled insulin dependent diabetes with glycaemia up to 150 mg/100 ml in first three hours after test, physical effort of variable intensity caused an individually variable fall in glycaemia from 15-43 mg/100 ml. In children with poorly controlled insulin dependent diabetes with hyperglycaemia from 210 to 300 mg/100 ml, physical effort caused a rise of glycaemia from 20-80 mg/100 ml compared to controls. Up to 3 hours after physical effort, 20 children had hypoglycaemia 60 mg 100 ml and 4 children had hypoglycaemia below 40 mg/100 ml. Hypoglykaemia manifested as a mild complex of clinical signs.
