Novel polymer substrates for SFM investigations of living cells, biological membranes, and proteins

Na⁺,K⁺-ATPase as the Target Enzyme for Organic and Inorganic Compounds

This paper gives an overview of the literature data concerning specific and non specific inhibitors of Na⁺,K⁺-ATPase receptor. The immobilization approaches developed to improve the rather low time and temperature stability of Na⁺,K⁺-ATPase, as well to preserve the enzyme properties were overviewed. The functional immobilization of Na⁺,K⁺-ATPase receptor as the target, with preservation of the full functional protein activity and access of various substances to an optimum number of binding sites under controlled conditions in the combination with high sensitive technology for the detection of enzyme activity is the basis for application of this enzyme in medical, pharmaceutical and environmental research.

Biochemical Functionalization of Polymeric Cell Substrata Can Alter Mechanical Compliance

Biochemical functionalization of surfaces is an increasingly utilized mechanism to promote or inhibit adhesion of cells. To promote mammalian cell adhesion, one common functionalization approach is surface conjugation of adhesion peptide sequences such as Arg-Gly-Asp (RGD), a ligand of transmembrane integrin molecules. It is generally assumed that such functionalization does not alter the local mechanical properties of the functionalized surface, as is important to interpretations of macromolecular mechanotransduction in cells. Here, we examine this assumption systematically, through nanomechanical measurement of the nominal elastic modulus of polymer multilayer films of nanoscale thickness, functionalized with RGD through different processing routes. We find that the method of biochemical functionalization can significantly alter mechanical compliance of polymeric substrata such as weak polyelectrolyte multilayers (PEMs), increasingly utilized materials for such studies. In particular, immersed adsorption of intermediate functionalization reagents significantly decreases compliance of the PEMs considered herein, whereas polymer-on-polymer stamping of these same reagents does not alter compliance of weak PEMs. This finding points to the potential unintended alteration of mechanical properties via surface functionalization and also suggests functionalization methods by which chemical and mechanical properties of cell substrata can be controlled independently.

Atomic force microscopy investigation of the dependence of cellular elastic moduli on glutaraldehyde fixation

Summary The atomic force microscope (AFM) has provided nanoscale analyses of surfaces of cells that exhibit strong adhesive and cell spreading properties. However, it is frequently reported that prior fixation is required for reliable imaging of cells with lower adhesive properties. In the present study, the AFM is used to assess the effects of fixation by glutaraldehyde on the elastic modulus of a human rhabdomyosarcoma transfectant cell line RDX2C2. Our results show a sharp increase in the elastic modulus for even mild fixation (0.5% glutaraldehyde for 60 s), accompanied by a dramatic improvement in imaging reproducibility. An even larger increase is seen in NIH-3T3 mouse fibroblasts, although in that case fixation is not typically necessary for successful imaging. In addition, our results suggest that treatment with glutaraldehyde restricts the content of the resulting images to features nearer to the cell surface.

Immobilization of Na, K-ATPase isolated from rat brain synaptic plasma membranes

Rat brain Na,K-ATPase partially purified by SDS from synaptic plasma membranes (SPM) was immobilized by adsorption on nitrocellulose (NC) polyvinylidene fluoride (PVDF) and glass fiber (GF) membranes. Partial SDS solubilization increased the enzyme activity by 40%. With regard to the preservation of the enzyme activity, nitrocellulose was shown to be the optimal support for the immobilization. The enzyme showed the highest percentage activity (14%) after 30 min of SPM adsorption, at 20?C under the vaccum, with 25 ?g of proteins per NC disc filter. In addition adsorption on NC stabilizes the Na,K-ATPase, since the activity was substantial 72 h after adsorption at 20?C. After adsorption, the sensitivity of the enzyme to HgCl2 and CdCl2 inhibition was higher. The results show that immobilized Na,K-ATPase SPMcan be used as a practical model for the detection of metal ions in different samples.