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PubMed1988

In vitro studies of fretting corrosion of orthopaedic materials.

Two models were used to study fretting corrosion of surgical alloys. In the first, the amount of load and motion between plates and screws was controlled, and corrosion rates of stainless steel and MP35N were determined by measurements of component weight loss and metal ion concentration in the test solutions. Stainless steel had the higher rate of fretting corrosion. The addition of 10% serum to saline resulted in a significant reduction of the corrosion rate of stainless steel and MP35N. The use of stainless steel screws in a mixed-metal combination with MP35N and titanium plates showed minimal effects on the performance of the stainless steel screws but an increase in fretting corrosion of the MP35N plates. In the second model, plates were applied to glass fiber-reinforced plastic tubes as bone analogues and subjected to cyclic axial loads. These results demonstrated a reduction in fretting corrosion rates associated with an increase in screw torque and a decrease in axial load. Corrosion rates were minimal with intact tubes simulating healed fractures and greatest with an oblique-cut fracture simulation. These models have proven useful for the evaluation of fretting corrosion rates of different alloys and for evaluation of variables such as fracture stability.

Alloys↗
PubMed1990

Fretting corrosion studies of universal femoral head prostheses and cone taper spigots.

Short-duration, cyclically loaded, axial, fretting corrosion tests were designed and performed to compare the fretting behaviour of different metal Howmedica universal heads connected to coated and uncoated metal cone taper spigots. Concurrent axial push-on and pull-off taper friction tests were also performed. There was no measurable fretting debris found in any test and SEM studies of the contact surfaces showed no evidence of fretting. It is concluded that no significant, long-term fretting corrosion of the Vitalium Co-Cr-Mo heads on the Vitallium or uncoated Ti-6AI-4V spigots, nor of the Orthinox stainless steel heads on the Orthinox spigots, is likely to occur in vivo.

Corrosion↗
PubMed1991

Cell association of fretting corrosion products generated in a cell culture.

The nature and distribution of corrosion products released into the body from orthopaedic implants remains an important issue. Various approaches to study this problem have been taken, such as the injection of metal salts, the injection of corrosion products, analysis of retrieved implants and adjacent tissue, and stimulated corrosion in vivo, with collection of body fluids and tissues for analysis. Tissue culture techniques have also been used to study the cellular response to metal salts or to corrosion or wear products that were generated in a separate environment. In this study, fretting corrosion of stainless steel plates and screws and of cobalt-chromium alloy plates with stainless steel screws was undertaken within a cell culture. The results showed that the cell cultures remained viable despite considerable metal ion release. Nickel was released in all cultures with fretting corrosion and was found mainly in the tissue culture medium (supernatant of the harvested cultures). Cobalt was detected only in those cultures with fretting corrosion of the cobalt-chromium alloy, and it was present mainly in the tissue culture medium. Chromium was released in all cultures with fretting corrosion, and it was found to be associated mainly with the cells with little in the culture medium. This compartmentalization of cell-associated chromium and fluid-associated cobalt and nickel supports in vivo studies showing chromium accumulation in red blood cells or tissue sites and comparatively low levels of nickel and cobalt.

Animals↗
PubMed1988

Effect of proteins and pH on fretting corrosion and metal ion release.

The objectives of this study were to determine the effect of proteins and protein charge on the corrosion of stainless steel. As Zwitter ions, proteins have a positive charge in solutions acidic to their isoelectric point (pI) and a negative charge in solutions basic to the pI. Fretting corrosion rates of stainless-steel plates and screws as determined by weight loss and metal ion release were studied in saline and protein solutions with the pH adjusted to 3, 5, and 8. Alterations in pH did not affect the corrosion rate in saline solutions. However, alterations of the pH in albumin solutions did affect the corrosion rate. In protein solutions acidic to the isoelectric point the presence of the positively charged albumin did not alter the corrosion rates as compared to that in saline. However, the presence of negatively charged proteins in solutions basic to their isoelectric points decreased the amount of corrosion. Thus, the effect of proteins on fretting corrosion is dependent on the charge on the protein. When the release of nickel was compared to the release of chromium, it was shown that the release was in proportion to the composition of the alloy when fretting corrosion took place in saline. The nickel/chromium ratio in the albumin and gamma globulin solutions was increased relative to that predicted indicating preferential release of nickel in protein solutions.

Animals↗
PubMed2025

FRET-FLIM for the Study of Protein-Protein Interactions Underpinning Mitosis Checkpoints.

Cell division is a key cellular process that ensures the continuation of life on Earth. In order to protect the genetic integrity of organisms, cell division must happen accurately, ensuring each daughter cell receives a complete copy of the original genome. The accuracy of this process is, in part, preserved by various cell cycle checkpoints. These checkpoints rely on the physical interactions of their components to ensure proper function. The spindle assembly checkpoint (SAC), for example, produces an inhibitory complex of BUBR1-BUB3 and MAD2 bound to CDC20. Many of these cell cycle checkpoint components have been identified in plants, but it has not yet been established whether plants have a mitotic checkpoint architecture that is similar to mammalian cells. To understand the function of plant cell cycle homologues, it is imperative to characterize their interactions in vivo. FRET-FLIM (Förster resonance energy transfer-fluorescence lifetime imaging microscopy), is a rapidly expanding technique that can be used to rapidly and simply characterize protein-protein interactions.

Fluorescence Resonance Energy Transfer↗
PubMed1992

Models of the actin monomer and filament from fluorescence resonance-energy transfer.

We have developed algorithms for combining fluorescence resonance-energy transfer (FRET) efficiency measurements into structural models which predict the relative positions of the chemical groups used in FRET. We used these algorithms to construct models of the actin monomer and filament derived solely from FRET measurements based on seven distinct loci. We found a mirror-image pair of monomer models which best fit the FRET data. One of these models agrees well with the atomic-resolution crystal structure recently published by Kabsch et al. in Heidelberg [Kabsch, W., Mannherz, H. G., Suck, D., Pai, E. F. & Holmes, K. C. (1990) Nature 347, 37-44]. The root-mean-square deviation between this FRET model and the crystal structure was about 0.9 nm. Other macromolecular models assembled from FRET measurements are likely to have a similar resolution. The largest discrepancy was for the Cys10 locus which deviated 1.44 nm from the crystal position. We discuss the limitations of the FRET method that may have contributed to this discrepancy, and conclude that the Cys10 FRET data have probably located Cys10 incorrectly in the FRET monomer model. Using the FRET monomer models, we found three orientations in the filament which best fit the intermonomer FRET data. These orientations differ substantially from the atomic-resolution filament model proposed by the Heidelberg group [Holmes, K., Popp, D., Gebhard, W. & Kabsch, W. (1990) Nature 347, 44-49], largely because of the discrepancies in the Cys10 data. These data should probably be excluded from the analysis; however, this would leave too few measurements to assemble a filament model. In the near future, we hope to obtain additional FRET measurements to other actin loci so that the filament modelling can be done without the Cys10 data.

Actins↗
PubMed1988

Electrochemical studies on the influence of proteins on the corrosion of implant alloys.

The effect of proteins on corrosion rates of 316L stainless steel, commercially pure titanium and titanium 6-aluminium 4-vanadium was studied in the static and fretting modes. The static mode was studied using cylindrical specimens as per ASTM F-746, and static fracture fixation plates. The fretting mode was studied using a two-hole plate fretting machine which caused a cyclic rocking motion between the plate and the screws, as per ASTM F-897. Electrochemical techniques of polarization resistance and Tafel slope measurements were used to study effects of proteins on the anodic and cathodic corrosion reactions. It was found that proteins increased the corrosion rate of the stainless steel and C.P. titanium cylindrical specimens, but did not have an effect on the Ti-6AI-4V cylinders. In the fretting mode proteins decreased the corrosion rate of the stainless steel plates, but did not have an appreciable effect on either of the titanium alloys. The presence of proteins appeared to cause an increase in the anodic Tafel constant and a decrease in the cathodic Tafel constant of stainless steel specimens. Significant differences in the shapes of the cathodic Tafel slopes were also seen with cylinders with different surface conditions, and static versus fretting plates.

Alloys↗
PubMed1991

On the relationship between distance information derived from cross-linking and from resonance energy transfer, with specific reference to sites located on myosin heads.

The techniques of fluorescence resonance energy transfer (FRET) and cross-linking can provide complementary information concerning the relative separation of a pair of sites. Cross-linking experiments provide an assessment of the distance of closest approach between a pair of sites. FRET measurements, by contrast, yield information about the average distance between the pair of sites. We have taken advantage of hybrid myosins to understand the relationship between distances obtained for a pair of equivalent sites, one on each myosin head, using both FRET (steady-state and time-decay) and cross-linking techniques. The rigid cross-linker, 4-4'-dimaleimidyl-stilbene-2-2'-disulfonic acid (DMSDS), can efficiently cross-link the two myosin regulatory light-chains, each at residue Cys50 of the Mercenaria regulatory light chain (Chantler, P.D., and S. M. Bower. 1988. J. Biol. Chem. 263:938-944), indicating that these sites can come within 18 +/- 2 A of each other. In a complementary set of experiments, steady-state and time-decay measurements using fluorescence donor/acceptor pairs located at these same sites indicate transfer efficiencies of somewhat less than 20%, suggesting an average separation of greater than 50 A between sites (Chantler, P. D., and T. Tao. 1986. J. Mol. Biol. 192:87-99). Here, we present theoretical calculations which show that efficient cross-linking can be achieved readily in dynamic systems such as the heads of myosin, even though the necessary subpopulation of proximate molecules at any instant may be below the detection limits of time-decay-FRET. Therefore, cross-linking experiments can provide important ancillary information about the extent of motions within a marcomolecular system when used in conjunction with FRET.As a corollary, demonstration of extensive cross-linking does not necessarily indicate a static proximity; the mean separation distance should be ascertained by other methods such as FRET.

Binding Sites↗
PubMed1992

Fluorescence resonance energy transfer analysis of the structure of the four-way DNA junction.

We have carried out fluorescence resonance energy transfer (FRET) measurements on four-way DNA junctions in order to analyze the global structure and its dependence on the concentration of several types of ions. A knowledge of the structure and its sensitivity to the solution environment is important for a full understanding of recombination events in DNA. The stereochemical arrangement of the four DNA helices that make up the four-way junction was established by a global comparison of the efficiency of FRET between donor and acceptor molecules attached pairwise in all possible permutations to the 5' termini of the duplex arms of the four-way structure. The conclusions are based upon a comparison between a series of many identical DNA molecules which have been labeled on different positions, rather than a determination of a few absolute distances. Details of the FRET analysis are presented; features of the analysis with particular relevance to DNA structures are emphasized. Three methods were employed to determine the efficiency of FRET: (1) enhancement of the acceptor fluorescence, (2) decrease of the donor quantum yield, and (3) shortening of the donor fluorescence lifetime. The FRET results indicate that the arms of the four-way junction are arranged in an antiparallel stacked X-structure when salt is added to the solution. The ion-related conformational change upon addition of salt to a solution originally at low ionic strength progresses in a continuous noncooperative manner as the ionic strength of the solution increases. The mode of ion interaction at the strand exchange site of the junction is discussed.

Base Sequence↗
PubMed1975

Nominal standard dose and tumor standard dose. Tables for radiation therapy planning and analysis.

The method of treatment planning for a predetermined NSD value is described in detail using various example-problems. The Fret tables allow the finding of the total number of fractions needed (NT) for the NSD. This is done through the NSD/d ratio, d standing for the fractional dose in rad. The Fret tables are for 1 to 7 fractions-per-week treatment schedules. The corresponding value of T (elapsed days) are shown for different week days of the therapy initiation with their respective Fret and NSD/d values. The handling of the rest and multi-rest periods is described. A method of finding the NSD value for a treatment which has reached the maximum connective tissue tolerance is described, covering even the most complex treatment plans. Fret-tumor tables for NSD-tumor and their use are described by appropriate example-problems. Ret equivalent therapy planning through direct NSD methods (Fret tables) and through an approximation method (tables provided) is described and the usage demonstrated by example-problems. The usage of parallel opposing and multiple portals is evaluated in ret-dose values (peripheral radiobiologic effect) and certain conclusions drawn to guide the therapist. These show in which situations all portals per session should be used and when alternate portals are more beneficial. The effect of portal weighting is included in this analysis. The application of ELLIS' NSD method for radium therapy is described. If, in the future, any changes in the power factors of the present NSD formula become necessary, the basic handling of the NSD problems described in this manuscript will remain unchanged. The values obtained from these tables can then be adjusted by the appropriate factors.

Cobalt Radioisotopes↗
PubMed1987

Fluorescence resonance energy transfer measurements of distances in actin and myosin. A critical evaluation.

The contractile proteins actin and myosin are of considerable biological interest. They are essential for muscle contraction and in eukaryotic cells they play a crucial role in most contractile phenomena. Over the years since the first fluorescence resonance energy transfer (FRET) paper appeared, an extensive body of literature has accumulated on this technique using actin, myosin and the actomyosin complex. These papers are reviewed with several aims in mind: we assess the reliability and consistency of intra- and inter-molecular distances measured between the fluorescent probes attached to specific sites on these proteins; we determine whether the measurements can be assembled into an internally consistent model which can be fitted to the known dimensions of the actomyosin complex; several of the FRET distances are consistent with the available structural data from crystallographic and electron microscopic dimensions; the modelled FRET distances suggest that the assumed value of the orientation factor (k2 = 2/3) is reasonable; we conclude that the model has a predictive value, i.e. it suggests that a small number of the published dimensions may be incorrect and predicts the magnitude of a larger number of measurements which have not yet been reported; and finally (vi) we discuss the contribution of FRET determinations to the current debate on the molecular mechanism of contraction.

Actins↗
PubMed1989

T-cell receptor-CD4 physical association in a murine T-cell hybridoma: induction by antigen receptor ligation.

By employing flow cytometric analysis and fluorescence resonance energy transfer (FRET), we examined the physical relationship between the T-cell receptor-CD3 complex (Ti-CD3) and the CD4 molecule on helper T cells. Through the use of an L3T4-negative murine T-cell hybridoma infectant expressing the human CD4 gene and having antigen specificity for HLA-DR, we show that binding of the Ti-CD3 complex with an anti-CD3 monoclonal antibody induces its redistribution proximal to cell-surface CD4. FRET efficiency was 9.4% on cells labeled with rhodaminated anti-CD3 and fluoresceinated anti-CD4. FRET was found to be temperature dependent, since similarly treated cells held at 4 degrees C displayed a FRET efficiency of less than 1%. Energy transfer was evident within 3 min after warming cells to 37 degrees C. Energy transfer was not detected between Ti-CD3 and the abundantly expressed leukocyte common antigen (CD45). Of greater significance was our observation that hybridomas infected with a truncated CD4 gene lacking the cytoplasmic domain failed to transfer energy despite the fact that CD4 was expressed on the cell surface at levels equivalent to or greater than the wild type. These studies suggest that after crosslinking of the Ti-CD3 on CD4+ T cells, a physical association occurs between the antigen receptor complex and CD4 and that the association is dependent upon the presence of the cytoplasmic domain of CD4.

Animals↗
PubMed1991

Structural interpretation of fluorescence resonance-energy transfer measurements.

Fluorescence resonance-energy transfer (FRET) has been widely used to determine distance information in macromolecular systems. However, little has been written about methods for combining FRET distances into coherent structural models. I argue that the methods used so far are inappropriate. This paper describes an algorithm specifically tailored for finding structures from FRET measurements. This algorithm finds structures which fit the experimentally measured parameter, the efficiency of energy transfer, rather than derived distances. The algorithm was implemented in Mathematica and applied to FRET distances obtained for the contractile protein actin. The approach used is applicable to other experimental techniques which measure distances between a relatively small number of loci.

Energy Transfer↗