Prostatic binding protein. A steriod-binding protein secreted by rat prostate.

Area of Science:

• Biochemistry
• Molecular Biology
• Urology

Background:

• Rat prostatic cytosol harbors a unique prostatic binding protein.
• This protein displays peculiar steroid-binding properties, including low affinity but measurable binding via charcoal adsorption.
• Binding is non-specific for steroids and significantly increases after delipidation.

Purpose of the Study:

• To characterize the prostatic binding protein found in rat cytosol.
• To investigate its steroid-binding properties and physicochemical characteristics.
• To confirm its secretion by the prostate and its concentration in prostatic fluid.

Main Methods:

• Charcoal adsorption assays for steroid-binding measurement.
• Delipidation of cytosol to enhance binding.
• Physicochemical characterization using ammonium sulfate precipitation, Sephadex G-100 gel filtration, sucrose density gradient centrifugation, and DEAE-cellulose chromatography.
• Polyacrylamide gel electrophoresis (PAGE) to assess binding activity and protein mobility.

Main Results:

• In delipidated cytosol, binding site concentration is 3.1 µmol/g protein with an apparent affinity for pregnenolone of 1.7 x 10^6 M^-1.
• Prostatic binding protein precipitates between 50-70% ammonium sulfate saturation.
• Molecular weight estimated at 51,000 Da by Sephadex G-100, sedimentation coefficient of 3.7 S, and eluted from DEAE-cellulose at 0.25 M KCl.
• Binding activity on PAGE aligns with the major cytosolic protein band, showing differential mobility compared to serum albumin based on gel concentration.

Conclusions:

• Prostatic binding protein is secreted by the prostate, as indicated by its high concentration in prostatic fluid.
• The protein possesses distinct physicochemical properties, including specific molecular weight, sedimentation, and chromatographic behavior.
• Its unique binding characteristics and high concentration suggest a significant role within the prostate.