Human plasma kallikrein, a vital enzyme, is not a single fixed size but exists in two main forms with molecular weights of 88 kDa or 85 kDa.
Kallikrein is a complex protein composed of different chains that are linked together. The variation in its size stems from the presence of two distinct light chain variants that can be part of the enzyme's structure.
Understanding Kallikrein's Molecular Composition
The molecular weight of human plasma kallikrein is determined by the combination of its primary structural components:
- Heavy Chain: This N-terminal part of the enzyme consistently has a molecular weight of 52,000 Daltons (52 kDa).
- Light Chain Variants: Two different versions of the light chain can bind to the heavy chain via disulfide bonds:
- One light chain variant weighs 36,000 Daltons (36 kDa).
- The other light chain variant weighs 33,000 Daltons (33 kDa).
The presence of either of these light chain variants, when combined with the heavy chain, results in the two possible molecular weights for the complete, active human plasma kallikrein molecule.
Molecular Weight Summary of Human Plasma Kallikrein Variants
| Component | Molecular Weight (Daltons) | Molecular Weight (kDa) |
|---|---|---|
| Heavy Chain | 52,000 | 52 |
| Light Chain (Variant A) | 36,000 | 36 |
| Light Chain (Variant B) | 33,000 | 33 |
| Total Kallikrein (Heavy + Light A) | 88,000 | 88 |
| Total Kallikrein (Heavy + Light B) | 85,000 | 85 |
This detailed breakdown illustrates why kallikrein's size is expressed as a range rather than a single value. These different forms of kallikrein play crucial roles in various biological processes, including blood pressure regulation, inflammation, and blood coagulation.
