Identification of substance P precursor forms in human brain tissue

Area of Science:

• Neuroscience
• Biochemistry
• Molecular Biology

Background:

• Substance P is a neuropeptide involved in various physiological processes.
• The existence and characterization of its prohormones in the human brain are not fully understood.

Purpose of the Study:

• To identify and characterize substance P prohormones in human brain extracts.
• To determine the molecular weight and potential structure of these prohormones.

Main Methods:

• Fractionation of acidic brain extracts using Sephadex G-50 chromatography.
• Enzymatic digestion with trypsin and a substance P-degrading enzyme.
• Isolation and quantitation of substance P(1-7) fragment via ion-exchange chromatography and radioimmunoassay.
• Structural confirmation using electrophoresis and High-Performance Liquid Chromatography (HPLC).

Main Results:

• Two polypeptide fractions with apparent molecular weights of 5,000 and 15,000 were identified.
• The 15,000 molecular weight component was the major fraction, though it represented only about 5% of total substance P radioimmunoassay activity.
• The size of the 15,000 component aligns with predicted sizes for substance P prohormones.

Conclusions:

• Substance P prohormones exist in human brain regions including the caudate nucleus, hypothalamus, and substantia nigra.
• The 15,000 molecular weight polypeptide is a strong candidate for the full-length substance P prohormone.
• Further studies are warranted to fully elucidate the structure and function of identified prohormones.