Scanning molecular sieve chromatography of interacting protein systems

The effect of bile salts on carbonic anhydrase

Bile salts are potent inhibitors of bovine carbonic anhydrase and human carbonic anhydrase I and human carbonic anhydrase II. To further characterize the binding of bile salts to carbonic anhydrase, rate constants for the CO2 hydration reaction in the presence of deoxycholate, cholate, glycocholate and taurocholate were determined using stop-flow experiments. Values for the Michaelis-Menton dissociation constant for bovine carbonic anhydrase, human carbonic anhydrase I and human carbonic anhydrase II were found to be 5.2, 9.2 and 13.2 mmol/L, respectively. The inhibition constant values for the various bile salts tested ranged from 0.1 to 1 mmol/L for bovine carbonic anhydrase, 1.6 to 2.4 mmol/L for human carbonic anhydrase I and 0.09 to 0.7 mmol/L for human carbonic anhydrase II. Our results suggest a mechanism of noncompetitive carbonic anhydrase inhibition for bile salts. Bile-salt binding to carbonic anhydrases as measured by scanning molecular sieve chromatography resulted in an increase in partition radius, molecular volume and surface area. The partition radius increased from 24 A to 28 A in the presence of 2.5 mmol/L sodium deoxycholate at critical micelle concentration. As determined by sedimentation equilibrium measurements, approximately 1 gm of carbonic anhydrase will bind 0.03 gm of deoxycholate, suggesting three to six binding sites for bile salt on the carbonic anhydrase molecule. The conformational changes and inhibition of carbonic anhydrases resulting from bile-salt binding may be important to the regulation of enzymatic activity in tissues along the enterohepatic circulation; by limiting bicarbonate availability this interaction may also contribute to the metabolic derangements seen in patients with cholestatic liver disease.

Interaction of human low density lipoprotein and apolipoprotein B with ternary lipid microemulsion. Physical and functional properties

Based on data from sedimentation velocity experiments, electrophoresis, electron microscopy, cellular uptake studies, scanning molecular sieve chromatography using a quasi-three-dimensional data display and flow performance liquid chromatography (FPLC), models for the interaction of human serum low density lipoprotein (LDL) and of apolipoprotein B (apo B) with a ternary lipid microemulsion (ME) are proposed. The initial step in the interaction of LDL (Stokes radius 110 A) with the ternary microemulsion (Stokes radius 270 A) appears to be attachment of the LDL to emulsion particles. This attachment is followed by a very slow fusion into particles having a radius of approx. 280 A. Sonication of this mixture yields large aggregates. Electron micrographs of deoxycholate-solubilized apo B indicate an arrangement of apo B resembling strings of beads. During incubation, these particles also attach to the ternary microemulsion particles and, upon sonication, spherical particles result which resemble native LDL particles in size. Scanning chromatography corroborates the electron microscopy results. By appropriate choice of display angles in a quasi-three-dimensional display of the scanning data (corrected for gel apparent absorbance) taken at equal time intervals during passage of a sample through the column, changes in molecular radius of less than 10 A can be detected visually. Such a display gives a quantitative estimate of 101 +/- 2 A for these particles (compared to 110 A for native LDL). The LDL-ME particles and apo B-ME particles compete efficiently with native LDL for cellular binding and uptake. Cellular association studies indicate that both LDL- and apo B-ME particles are effective vehicles for lipid delivery into cells.

Scanning molecular sieve chromatography of interacting protein systems: nonlinear least-squares analysis of small zone experiments

A simple routine for nonlinear least-squares analysis is applied to small zone scanning data, where calibration of the gel column requires the use of fully characterized markers of known molecular size. Application of nonlinear least-squares analysis eliminates the difficulty encountered because of scarcity of calibrating markers for gels whose porosities span certain size ranges by providing a sensitive measure of changes in molecular size of the interacting protein system, in order to determine the interaction parameters, size heterogeneity, and the centroid position for time difference chromatographic experiments.

A simple method of analyzing profiles in time-difference direct optical scanning gel chromatography

A simple method is presented for the analysis of time-difference, large-zone chromatography profiles. The method is derived from basic theory and is applicable to multicomponent as well as single-component systems. Simple computer simulations are used to demonstrate the inaccuracies of earlier, more empirical methods. This method has been tested on several proteins using an inexpensive, semi-automated, data acquisition and control system.

Interaction of human serum apolipoprotein B with sodium deoxycholate

Preparation of apolipoprotein B (Apo B)-deoxycholate (DOC) complexes by gel filtration chromatography in the presence of 20 mM DOC, pH 8.5, gave two populations of particles with 5% (peak I) and 13% (peak II) lipid remaining bound. These complexes were initially shown to be very large and elongated, with partition radii of approx. 131 +/- 0.5 A, weight average molecular weights of approx. 164 000 +/- 1 000, and an intrinsic viscosity of 80.19 +/- 2.21 ml/g. Additionally, they appeared very similar to native low-density lipoprotein on sodium dodecyl sulfate-polyacrylamide gels, giving one major band. Incubation of these samples for 10 days under nitrogen at 4 degrees C in the presence of antibiotics and protease inhibitor resulted in dissociation to many smaller subunits. Results of scanning molecular sieve chromatography and analytical ultracentrifugation showed that dissociation of these complexes was relatively slow and indicated the presence of at least two classes of components in fresh samples: one a very elongated complex with a radius directly correlated to the DOC/Apo B ratio and inversely correlated to sample aging; and another of much smaller radius which was independent of DOC/Apo B ratio but directly correlated to sample aging; indicating that these dissociated subunits interact with each other to an appreciable extent. Furthermore, these complexes were found to undergo a preferential hydration upon interaction with DOC, which may contribute to large changes in their effective specific volumes, as well as to dissociation of subunits.

Iron content and molecular weight of uteroferrin and a comparison of its iron and copper forms

The molecular weight of the purple, iron-containing glycoprotein uteroferrin has been determined to be 35140 +/- 1610 by sedimentation equilibrium centrifugation. This is consistent with measurements carried out by other procedures. The dry weight of a solution of uteroferrin with an absorption of 1.00 cm -1 at 280 nm was 0.87 mg/ml. Highly purified uteroferrin has a ratio of absorbance at 280 nm to 545 nm of about 13.2 and a revised extinction coefficient at 545 nm of 3.1 . 10(3) M -1 is presented. The iron content of uteroferrin has been determined both colorimetrically and by atomic absorption spectroscopy. One iron atom is present per polypeptide chain. Reduction with dithionite leads to loss of iron, allowing the apoprotein to be prepared. Enzymatic activity can be restored to the apoprotein with Fe(III) or with Cu(II). The copper enzyme has no visible color and has a higher pH optimum than the Fe-uteroferrin. Whereas the phosphatase activity of the latter is increased several-fold by beta-mercaptoethanol, reduction inactivates Cu-uteroferrin. Both forms of uteroferrin have similar Km values for p--nitrophenyl phosphate and are inhibited by molybdate but not by tartrate. Excess Cu(II) and Fe(III) strongly inhibit uteroferrin phosphatase activity and these results may explain the failure of other to restore activity to the apoprotein using Cu(II) and Fe(III) salts.

Time difference scanning gel chromatography: Computer simulations

The time difference profile method of gel scanning chromatography developed by Brumbaugh, Saffen and Chun (Biophysical Chemistry, 1979) has been examined by computer simulation. The method is found to produce values for centroid movements that mimic those of the system being examined but are not quantitatively correct. In all cases the time differential "centroid" is larger than that of the concentration derivative (true) centroid and move at a rate slightly faster than the true centroids. This faster rate slowly decreases towards the true rate but does not approach it within reasonable times. This distorted movement reflects the distorted emphasis given to the larger species in the time differential method. The time difference method has been shown to give an adequate measure of the axial dispersion coefficient, L, for single species systems.