Kallikrein is the Proteolytic Enzyme Present in Saliva
Among the options provided, kallikrein (option 3) is the proteolytic enzyme present in saliva. 1
Understanding the Enzyme Classification
The key to answering this question lies in understanding which of these enzymes has proteolytic activity (protein-digesting capability):
Non-Proteolytic Enzymes in Saliva
Ptyalin (salivary amylase): This is a carbohydrate-digesting enzyme, not a proteolytic enzyme—it breaks down starch, not proteins 2
Lipase: This enzyme digests lipids (fats), not proteins, though it is present in saliva 2
Enzymes with Proteolytic Activity
Lysozyme: While present in saliva as an antimicrobial agent, lysozyme is not classified as a proteolytic enzyme 2. Its primary function is muramidase activity (breaking down bacterial cell walls by hydrolyzing peptidoglycan), not general protein digestion 3, 4. Although it can affect some proteins under specific conditions, this is not its primary enzymatic function.
Kallikrein: This is specifically identified as a proteolytic enzyme that is secreted by mucosal glands and present in saliva 1. Unlike albumin which simply diffuses into mucosal secretions, kallikrein is actively secreted and has true proteolytic (protein-digesting) activity 1.
Important Clinical Context
Proteolytic enzymes in saliva primarily originate from oral bacteria rather than being major components of human salivary secretion 2. These bacterial proteolytic enzymes can degrade salivary proteins including immunoglobulins, albumin, lysozyme, mucin, lactoferrin, and lactoperoxidase 5. This is why protease inhibitors are recommended when collecting saliva samples for research purposes 2.
Key Distinction
The question asks specifically about a proteolytic enzyme present in saliva, not necessarily one that is the most abundant or clinically significant. Kallikrein meets this criterion as a true proteolytic enzyme that is actively secreted into saliva 1.
Human saliva does contain some endogenous proteolytic activity at various pH levels (pH 3.5,7.5-8.0, and 9.3), though the specific enzymes responsible vary by location and substrate 6.