Complement fixation for study of placental-type alkaline phosphatase

Area of Science:

• Biochemistry
• Immunology

Background:

• Human placental alkaline phosphatase (PLAP) exists in multiple forms.
• Understanding the structural basis of PLAP isoenzymes is crucial for biochemical and immunological studies.

Purpose of the Study:

• To compare human placental alkaline phosphatase preparations with different specific enzyme activities.
• To investigate the relationship between enzyme activity and immunoreactivity using microcomplement fixation assays.

Main Methods:

• Microcomplement fixation assays were performed on PLAP preparations with varying specific enzyme activities.
• Monospecific antisera were used to quantify immunoreactive enzyme protein.
• Ampholine isoelectric focusing was employed to separate PLAP into different forms (A and B).

Main Results:

• Both specific enzyme activity and complement fixation units increased 15,000-fold upon purification.
• The ratio between complement fixation units and specific enzyme activity remained constant throughout purification.
• Separated PLAP forms (A and B) exhibited the same ratio of immunoreactive enzyme protein to enzyme activity.

Conclusions:

• Complement fixation units correlate directly with specific enzyme activity in PLAP.
• Microcomplement fixation assays with monospecific antisera are effective for analyzing structural variations among alkaline phosphatase isoenzymes.