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A new method for the determination of dissociation constant (kd) on the binding of CA19-9 to its antibody in type 2diabetic patients by enzyme linked immunosorbent assay (ELISA) with some modifications.
Authors : Russul R. Al-Hamaoy, D. Hassan H. AL-Saeed, Dr. Mahmood Shakir Khudhair
Background:-In order to quantify the interactions between molecules of biological interest, the determination of dissociation constants (Kd) is essential. Several methods are known for calculating these constants, most of which are based on linearization procedures, such as the Scatchard (1949) plot, Lineweaver and Burk (1934) plot, etc. This linearization does not require direct ligand labelling or the absolute concentration of the complex and is, therefore, especially suitable for Kd determination from an enzyme-linked immunosorbent assay (ELISA). Objectives: - Present a new method for the determination of a dissociation constant (Kd) of the binding of CA19-9 to its antibody in type 2 diabetic patients using Scatchard plot through development of ELISA. Methods:- This study included eighty individuals with mean age (46.5 ± 1.14 years) were divided into two groups. Group Ⅰ,forty patients with type Ⅱ diabetes mellitus have a mean duration 6.6± 0.94.Group Ⅱconsisted of forty healthy individuals were classified as control group. CA19-9 level were measured in serum by ELISA technique.Select the highest value from the first group and other value within the normal range chosen from the second group in addition to the CA19-9 standard (100U/ml) to determine the dissociation constant (kd) using external CA19-9 monoclonal antibody and calculated by Scatchard plot. Results:- The dissociation constant of the interaction between antibody and antigen from the data of direct, non-competitive enzyme linked immunosorbent assays (ELISA) by Scatchard plot is (15.6006, 12.5313 and 4.1271 U/ml) for Standard (100 U/ml), Patient (99.568 U/ml) and Control (23.494 U/ml) respectively. Conclusion:-A simple linearization procedure developed to determine the dissociation constant of the interaction between antibody and antigen from the data of direct, non-competitive enzyme linked immunosorbent assays (ELISA) by Scatchard plot.

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April 2016