Isolation of cathepsin D from human leucocytes

Area of Science:

• Biochemistry
• Cell Biology
• Immunology

Background:

• Proteases play crucial roles in cellular functions.
• Leukocytes, key immune cells, contain various enzymatic activities within their granules.
• Understanding protease localization and characteristics in different leukocyte types is essential for immunology and disease research.

Purpose of the Study:

• To investigate and characterize acid and neutral protease activities in human blood leukocytes.
• To differentiate protease profiles between mononuclear and polymorphonuclear leukocytes.
• To purify and identify the acid protease found in leukocytes.

Main Methods:

• Separation of human blood leukocytes using discontinuous density gradient centrifugation.
• Assay of acid and neutral protease activities in isolated granule fractions.
• Enzyme separation and purification using DEAE chromatography and Sephadex G-200 gel chromatography.
• Characterization of purified enzyme by optimum pH, molecular weight determination, and disc-gel electrophoresis.

Main Results:

• Mononuclear leukocytes exhibited only acid protease activity.
• Polymorphonuclear leukocytes displayed predominant neutral protease activity with a minor acid protease peak.
• A distinct acid protease was purified over 400-fold from mixed leukocytes.
• The purified acid protease demonstrated an optimum pH of 3.6, a molecular weight of 42,000 Da, and was identified as cathepsin D.

Conclusions:

• Human leukocyte granule fractions contain distinct acid and neutral protease activities.
• Cathepsin D is identified as the primary acid protease in human leukocytes.
• The differential distribution of proteases in leukocyte subsets suggests specific functional roles.