Determination of the glass-transition temperature of proteins from a viscometric approach.

All fully hydrated proteins undergo a distinct change in their dynamical properties at glass-transition temperature Tg. To determine indirectly this temperature for dry albumins, the viscosity measurements of aqueous solutions of human, equine, ovine, porcine and rabbit serum albumin have been conducted at a wide range of concentrations and at temperatures ranging from 278 K to 318 K. Viscosity-temperature dependence of the solutions is discussed on the basis of the three parameters equation resulting from Avramov's model. One of the parameter in the Avramov's equation is the glass-transition temperature. For all studied albumins, Tg of a solution monotonically increases with increasing concentration. The glass-transition temperature of a solution depends both on Tg for a dissolved dry protein Tg,p and water Tg,w. To obtain Tg,p for each studied albumin the modified Gordon-Taylor equation was applied. This equation describes the dependence of Tg of a solution on concentration, and Tg,p and a parameter depending on the strength of the protein-solvent interaction are the fitting parameters. Thus determined the glass-transition temperature for the studied dry albumins is in the range (215.4-245.5)K.

Association between hemorheological alteration and clinical diagnosis of metabolic syndrome among patients qualified for bariatric surgery.

This study presents the association between metabolic syndrome and hemorheological parameters among obese patients qualified for bariatric surgery. We studied 73 morbidly obese patients who were qualified for bariatric surgery. Blood and plasma viscosity measurements were performed using a cone-plate viscometer (Brookfield DV-II). RBC aggregation was measured using the Laser-assisted Optical Rotational Cell Analyser (LORCA). The following parameters for the aggregation process were estimated: aggregation index (AI), amplitude (AMP), aggregation half-time (t1/2), threshold shear rate (γthr), the fast (Tfast) and the slow (Tslow) component. Metabolic syndrome was defined according to the Adult Treatment Panel III and International Diabetes Federation criteria. The obese presented differences in all rheological properties compared to control, regardless of clinical diagnosis of metabolic syndrome, except that whole blood viscosity was higher only in the obese metabolic syndrome group. No differences among the obese with and without metabolic syndrome were observed except in hematocrit. Whole blood viscosity and corrected blood viscosity correlated positively with WHR and BMI. AI, γthr, Tslow correlated positively with BMI, WHR, total cholesterol level and low-density lipoproteins. Negative correlation presented t1/2 with BMI, WHR, fibrinogen, total cholesterol level and low-density lipoproteins. The study showed that morbid obesity is associated with hemorheological disturbances independently of clinical diagnosis of metabolic syndrome.

A viscometric approach of pH effect on hydrodynamic properties of human serum albumin in the normal form.

The paper presents the results of viscosity determinations on aqueous solutions of human serum albumin (HSA) at isoelectric point over a wide range of concentrations and at temperatures ranging from 5°C to 45°C. On the basis of a modified Arrhenius equation and Mooney's formula some hydrodynamic parameters were obtained. They are compared with those previously obtained for HSA in solutions at neutral pH. The activation energy and entropy of viscous flow and the intrinsic viscosity reach a maximum value, and the effective specific volume, the self-crowding factor and the Huggins coefficient a minimum value in solutions at isoelectric point. Using the dimensionless parameter [η]c, the existence of three ranges of concentrations: diluted, semi-diluted and concentrated, was shown. By applying Lefebvre's relation for the relative viscosity in the semi-dilute regime, the Mark-Houvink-Kuhn-Sakurada (MHKS) exponent was established. The analysis of the results obtained from the three ranges of concentrations showed that both conformation and stiffness of HSA molecules in solutions at isoelectric point and at neutral pH are the same.

Temperature behaviour of viscous flow with proteins.

The paper presents the results of viscosity determinations on aqueous solutions of different mammalian serum albumins at a wide range of concentrations and at temperatures ranging from 278 K to 318 K. On the basis of these measurements and a modified Arrhenius equation, the functional dependence of the solution activation energy of viscous flow on temperature was established. The analysis of the results obtained shows that the activation energy decreases with increasing temperature according to a square function for solutions, water molecules, and the albumins studied. The rate at which the activation energy decreases with increasing temperature is different for each albumin and mainly depends on its hydrodynamic radius.

A comparison of solution conformation and hydrodynamic properties of equine, porcine and rabbit serum albumin using viscometric measurements.

This paper presents the results of viscosity determinations on aqueous solutions of equine, porcine and rabbit serum albumin over a wide range of concentrations and at temperatures ranging from 5 degrees C to (42-45) degrees C. The results are compared with human and bovine serum albumin previously studied. Viscosity-temperature dependence is discussed on the basis of the modified Arrhenius formula. The effective specific volume, the activation energy and entropy of viscous flow for all investigated albumins are compared. Viscosity-concentration dependence, in turn, is discussed on the basis of Mooney equation. Based on the assumption that theoretical and experimental values of Simha factor--at high temperature limit--are equal to each other, the hydrodynamic volume of the studied albumins has been calculated. The numerical values of a self-crowding factor were also obtained. At low concentration limit, the numerical values of the intrinsic viscosity and of Huggins coefficient were compared.

Determination of some hydrodynamic parameters of ovine serum albumin solutions using viscometric measurements.

The influence of protein concentration and temperature on the viscosity of ovine serum albumin (OSA) solutions was studied. The Mooney equation and a modified Arrhenius formula were used to described the viscosity-concentration and viscosity-temperature dependence of the solutions, respectively. The effective specific volume, the activation energy and entropy of viscous flow for hydrated OSA were calculated. The axial ratio and the dimensions of the main semi-axes of hydrated OSA were established. At low concentration limit, the temperature dependence of the intrinsic viscosity and Huggins coefficient is presented. Comparison of some hydrodynamic parameters obtained for different proteins has been made.

On the hydrodynamics and temperature dependence of the solution conformation of human serum albumin from viscometry approach.

The paper presents the results of viscosity determinations on aqueous solutions of human serum albumin (HSA) at a wide range of concentrations and at temperatures ranging from 5 to 45 degrees C. On the basis of a modified Arrhenius formula and Mooney's equation, the viscosity-temperature and viscosity-concentration dependence of the solutions are discussed. The effective specific volume, the activation energy and entropy of viscous flow for hydrated HSA were calculated. Different models of HSA molecule are discussed and the best one-from the hydrodynamic point of view-was established. At low concentration limit, such rheological quantities as the intrinsic viscosity and Huggins coefficient were obtained. Using the dimensionless parameter [eta]c, the existence of three characteristic ranges of concentrations: diluted, semi-diluted and concentrated, was shown.