Is alkaline phosphatase biomimeticaly immobilized on titanium able to propagate the biomineralization process?

Tissue-nonspecific alkaline phosphatase (TNAP) is a key enzyme in the biomineralization process as it produces phosphate from a number of phospho-substrates stimulating mineralization while it also inactivates inorganic pyrophosphate, a potent mineralization inhibitor. We have previously reported on the reconstitution of TNAP on Langmuir monolayers as well as proteoliposomes. In the present study, thin films composed of dimyristoylphosphatidic acid (DMPA) were deposited on titanium supports by the Langmuir-Blodgett (LB) technique, and we determined preservation of TNAP's phosphohydrolytic activity after incorporation into the LB films. Increased mineralization was observed after exposing the supports containing the DMPA:TNAP LB films to solutions of phospho-substrates, thus evidencing the role of TNAP on the growth of calcium phosphates after immobilization. These coatings deposited on metallic supports can be potentially applied as osteoconductive materials, aiming at the optimization of bone-substitutes integration in vivo.

Pendant-drop method coupled to ultraviolet-visible spectroscopy: A useful tool to investigate interfacial phenomena.

UV-vis spectroscopy is a powerful tool to investigate surface phenomena. Surface tension measurements coupled to spectroscopic techniques can help to elucidate how the interface organization influences the electronic properties of molecules. However, appreciable sample volumes are usually necessary to achieve strong signals during conduction of experiments. This study reports on the simultaneous acquisition of surface tension data and UV-vis spectra by axisymmetric drop shape analysis (ADSA) coupled to diffuse reflectance (DRUV) spectrophotometry using a pendant microliter-drop that requires small sample volumes and low analyte concentrations. Three example systems gave evidence of the applicability of this technique: (a) disaggregation of an organic dye driven by surfactant as a function of the surface tension and alterations in the UV-vis spectra, (b) activity of a glycosylphosphatidylinositol anchored enzyme estimated from formation of a colored product, and (c) interaction between this enzyme and biomimetic membrane systems consisting of dipalmitoylphosphaditylcholine and cholestenone. Apart from using smaller sample volume, this coupled technique allowed to investigate interfacial organization in the light of electronic spectra obtained in loco within a shorter acquisition time. This procedure provided precise interfacial information about static and dynamic systems. This has been the first study describing the kinetic activity of an enzyme in the presence of phospholipid monolayers through simultaneous determination of the surface tension and UV-vis spectra.