Leo D. Kahn

Piezoelectricity in collagen films

SummaryTissue collagen exhibits several levels of structural organization, and this complicates efforts to determine the origin of its piezoelectricity. We made collagen films—by evaporation and electrodeposition from solution—and examined the relation between collagens piezoelectricity and its electron microscopic appearance. We found that the electrodeposited films were more organized and exhibited higher piezoelectric coefficients than the evaporated films. Despite this, the evaporated films were piezoelectric, thereby suggesting that the effect originates either at the level of the tropocollagen molecule or, at most, with aggregated structures no larger than 50 Å in diameter.

The electric birefringence buildup curve as applied to the determination of the dipole moment of soluble collagen

Abstract Electric birefringence patterns of calfskin corium collagen dissolved in citrate buffer in the acid pH range were made. At high concentrations of collagen, these showed an anomalous electric birefringence pattern which was indicative of time-dependent variations in permanent and induced dipole moments. Measurements of dipole moments showed that when the square wave pulsed electric field is created, permanent and induced dipole moments are in the same direction. This is followed by a progressive decrease in permanent dipole moment with pulse duration, and at high field strength the electric field eventually brings about a reversal in direction between permanent and induced dipole moments. The effect of pH on this phenomenon was studied.

Some effects of electrolytes on collagen in solution

Abstract Since collagen form an aqueous solution only when electrolytes are present, a study of the effects of electrolytes on dissolved collagen was carried out to obtain data which might lead to improved solubilization and fractionation techniques. Salting-out curves of collagen in phosphate buffer solutions were prepared. Dissolved collagen was constituted from phosphate buffer and citrate buffer solutions by various methods and the precipitated fibrils showed a variety of structural forms. Fibril morphology was related to solution history and an attempt was made to show that electrolytic environment influenced the aggregation of collagen molecules into organized structures through ion binding and electrostatic interaction.

Electric birefringence of bacterial flagellar protein filaments: Evidence for field-induced interactions

The time course for the build-up and decay of birefringence induced by a rectangular voltage pulse was measured on solutions of flagellar filaments from Salmonella equi-abortus (strain SJ25). These filaments are tubular polymers of protein (degree of polymerization ≈ 103) constituted by non-covalent linkage of flagellin monomers of molecular weight 4 × 104. The effect on electro-optical properties of solutions of filaments due to variations in temperature, concentration and mean length of protein filaments, and the duration and intensity of the applied electric field is described. Analysis of the field intensity dependence of the birefringence and comparison of the build-up and decay processes indicate that orientation in the field is due primarily to the existence of a permanent dipole moment in the filaments. At 18 °C the following values were obtained for a solution of filaments with mean length and standard deviation of 0.39 and 0.30 μm: specific Kerr constant (Ksp) = 6.14 × 10−3 electrostatic units; optical anisotropy factor (g1 — g2) = 5.66 × 10−3; dipole moment (μ) = 1.01 × 105 Debye units; and mean relaxation time (\gt) = 9.20 ms. At temperatures below 20 °C there is a marked increase in the optical anisotropy factor of the filaments which may be due to a change in their flexibility. The large values of Ksp obtained indicate the highly responsive nature of these filaments to an electric field. The birefringence decay curves were decomposed by computer into a specified number of exponential terms from which both the mean length and the size distribution of these polydisperse filaments were calculated. The results obtained were in substantial agreement with the values of these parameters observed by electron microscopy. A cumulative field effect dependent on field intensity and filament concentration was observed. Repeated pulsing of electric field, above threshold values of field intensity and filament concentration, produced decreases in the birefringence near 60% of its initial value. The effect was reversible with a time constant greater than two minutes. No appreciable change in the relaxation time for decay of birefringence was observed on multiple pulsing of these solutions. These results are interpreted consistently to arise from the sidewise aggregation of filaments induced by electrical impulses of sufficient intensity and duration. These properties appear relevant to bacterial motility: variations in electric potential along the membrane of the bacterium might serve first to orient these organelles and then to induce their coalescence to “bundles” of filaments. The latter structures are commonly observed in vivo. In this way the activity of flagella might be co-ordinated.

The effects of an electric field on soluble collagen

Electric birefringence decay curves of collagen suspended in aqueous buffered media were plotted as functions of pulse width and amplitude. They were then resolved into two components by means of an analog simulator. When these data were combined with the results of repeated pulsing, it was shown that an electric field promotes aggregation of collagen, although the variety of aggregate sizes falls within a fixed range. Observations of electric birefringence of dissolved collagen preparations as a function of ionic strengths tend to indicate that the bonding that occurs in an electric field is electrostatic.

The positively cooperative binding of concanavalin a to corn starch: The isotherm of binding and a measure of the cooperativity

Abstract The binding of concanavalin A to corn starch was investigated by fluorimetric assay. The extent of binding varied linearly with the mass of ligand, and followed a hyperbolic law with respect to the mass of starch. This led to an isotherm of binding: r = 0.33A o ME o −0.88 , where r is the extent of binding, A o is the mass of concanavalin A present (both bound and unbound), and M o is the mass of starch. These results, and Scatchard plots of the data, showed the binding to be positively cooperative. The exponent of the M o term was shown to be a measure of cooperativity. The binding was dependent on the ionic strength of the dispersion medium, and this indicated that the binding may have an electrostatic component.