Question

Precipitation of Albumin and ?-Globulin from Blood Plasma Explain the solubility principles involved in the precipitation of albumin and ?-globulin from blood plasma by the Cohn process.

Short answer

The Cohn process precipitates proteins from blood plasma by using changes in temperature and ionic strength to alter the solubility of the proteins. Fibrinogen and ?-globulin precipitate out first at cold temperatures and low ionic strength. The remaining supernatant, containing albumin and other proteins, is separated and subjected to a higher ionic strength, at which ?-globulin precipitates. Finally, ethanol is added to precipitate the remaining proteins, including albumin. This process of selective precipitation allows the different proteins to be separated and extracted.

Step-by-step solution

Understand the Basics of The Cohn Process

The Cohn process refers to the method used to precipitate and extract various proteins from blood plasma. This process relies heavily on the different solubility properties of these proteins in blood plasma. Physiological parameters such as pH, temperature, and ionic strength, all of which can be altered to bring about the selective precipitation.

Precipitation Principles

Precipitation refers to the process by which soluble substances are converted into an insoluble form. This usually occurs due to changes in temperature, pressure or the presence of a specific reagent. For proteins, precipitation typically results from changes in the pH, temperature, or ionic strength of the solution. These changes can disrupt the normal interactions between the protein and the surrounding water molecules, causing the protein to become less soluble and eventually precipitate out of the solution.

The Precipitation of Albumin and ?-Globulin

At cold temperatures and low ionic strength, almost all plasma proteins remain dissolved except fibrinogen and ?-globulin, which precipitate out. The albumin, ?-globulins, and other proteins continue to be in the supernatant, which is separated from the precipitate and subjected to an increased ionic strength. At this stage, ?-globulin becomes less soluble and precipitates out. Finally, when ethanol is gradually added, remaining proteins including albumin precipitate. By exploiting these differences in solubility, the Cohn process allows for the selective precipitation and extraction of albumin and ?-globulin.

Conclusion

Thus, the Cohn process exploits the different solubility properties of the plasma proteins at different conditions of cold temperatures and ionic strength to bring about the selective precipitation of proteins such as albumin and ?-globulin.

Key concepts

Protein Precipitation

Protein precipitation is a critical process used to separate and purify proteins from a complex mixture. When proteins are precipitated, they transition from a soluble to an insoluble form. This process plays a vital role in the preparation of proteins for analysis and utilization.

Factors such as pH, temperature, and ionic strength can induce protein precipitation because they affect the protein's stability and solubility. Proteins have a specific pH value at which their net charge is zero, known as the isoelectric point (pI). Around this pH range, proteins tend to aggregate and precipitate since there's minimal electrostatic repulsion preventing them from coming together.

Temperature changes can also induce precipitation. Typically, raising the temperature increases protein solubility, but in some cases, particularly with drastic temperature changes, it can cause denaturation and subsequent precipitation. On the other hand, adjustments in ionic strength can shield or promote the interaction of charged groups on the protein's surface, influencing solubility and precipitation.

By manipulating these factors, the Cohn process achieves the selective precipitation needed for protein purification. A clear understanding of these principles enables scientists to isolate specific proteins according to their unique characteristics.

Plasma Protein Solubility

Plasma protein solubility is dependent on multiple physicochemical properties that influence how proteins behave in a solution. These proteins, like albumin, globulins, and fibrinogen, each have unique solubility profiles which are crucial in biological processes and biotechnologies.

The solubility of plasma proteins can be affected by their conformation, which in turn, can be influenced by environmental conditions such as pH and the presence of various ions or solvents. For instance, in the blood stream under physiological conditions, proteins are stable and soluble. However, when subjected to altered pH levels, temperature or ionic conditions, their solubility can decrease, leading to precipitation.

The Cohn process takes advantage of the differential solubility of plasma proteins at varying ionic strengths and temperatures. An increase in ionic strength, through the addition of certain salts or changes in pH, can lead to controlled precipitation of specific proteins without affecting others. Similarly, temperature regulation can target temperature-sensitive proteins. Understanding these solubility principles is essential for the effective extraction and purification of albumin and ?-globulin during plasma processing.

Albumin and ?-globulin Extraction

The extraction of albumin and ?-globulin is a refined example of how variations in protein solubility can be exploited for protein purification. Albumin and ?-globulin are two major types of proteins found in blood plasma, each serving important physiological functions.

To selectively extract these proteins, conditions are induced where other plasma components precipitate while the desired proteins remain in solution. Initially, ethanol is used at low temperatures to precipitate contaminants while albumin and ?-globulins stay soluble. Upon adjusting the ethanol concentration and ionic strength, ?-globulin's solubility decreases and it precipitates; albumin stays in solution until precise conditions for its precipitation are established.

This stepwise process reflects the fundamental solubility characteristics of each protein. It also strikes a balance between purity and yield, factors that are crucial in the pharmaceutical and medical industries, where these proteins have applications in therapeutics and as diagnostic tools. Thorough knowledge of the solubility properties of albumin and ?-globulin, and how to manipulate them, is crucial in the Cohn process to achieve their successful extraction.