What Does the Casein Test Detect?
The casein test is a laboratory assay that detects and measures proteolytic enzyme (protease) activity by using casein protein as a substrate.
Primary Function
The casein test fundamentally measures the ability of proteases to break down casein protein, which serves as an indicator of proteolytic activity in various contexts 1, 2, 3.
Specific Applications
Protease Activity Measurement
- Detects the presence and quantifies the activity of proteolytic enzymes including trypsin, chymotrypsin, elastase, subtilisin, thermolysin, papain, and proteinase K 2, 3, 4
- Measures enzyme activity across a wide pH range (pH 2.0 to 11.0), making it versatile for different enzyme types and conditions 4
- Quantifies protease inhibitor activity by measuring the reduction in casein degradation when inhibitors are present 1
Bacterial Proteolytic Systems
- Identifies bacterial protease production in clinical microbiology, particularly for oral pathogens like Porphyromonas gingivalis and Treponema denticola that use proteolytic activity as a virulence mechanism 4
- Characterizes bacterial proteolytic pathways such as those used by Lactococcus lactis to degrade beta-casein for amino acid acquisition 5
Technical Methodology
The test employs various labeled forms of casein:
- Fluorescamine-labeled casein for fluorometric detection, capable of quantitating approximately 0.05 μg of trypsin 2
- Fluorescein isothiocyanate (FITC)-labeled casein for measuring proteases in the nanogram to subnanogram range 3
- BODIPY-alpha-casein for pH-independent fluorescence polarization assays with real-time kinetic measurements in 1-5 minutes 4
- Biotinylated casein for solid-phase assays using alkaline phosphatase-streptavidin detection systems 1
Clinical Context
While casein testing is primarily a research and industrial tool for enzyme characterization, it has limited direct clinical diagnostic applications. It should not be confused with clinical tests that happen to use casein as a control substrate (such as in fibrinolysis assays where casein serves as an alternative substrate for plasmin activity measurement 6).