When the amino acid sequences of several Bence-Jones proteins (light chains) from different individuals were compared, a striking pattern emerged. The amino-terminal half of the chain, consisting of 100-110 amino acids, was found to vary among different Bence-Jones proteins. This region was called the variable (V) region. The carboxyl-terminal half of the molecule, called the constant (C) region, had two basic amino acid sequences. This led to the recognition that there were two light chain types, kappa (k) and lambda (X). In humans, 60% of the light chains are kappa and 40% are lambda, whereas in mice, 95% of the light chains are kappa and only 5% are lambda. A single antibody molecule contains only one light chain type, either k or X, never both.
The amino acid sequences of X light chains show minor differences that are used to classify X light chains into subtypes. In mice, there are three subtypes (X1, X2, and X3); in humans, there are four subtypes. Amino acid substitutions at only a few positions are responsible for the subtype differences.
Was this article helpful?
This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.