Steroidogenesis-activator polypeptide isolated from a rat Leydig cell tumor

Area of Science:

• Biochemistry
• Endocrinology
• Molecular Biology

Background:

• A cycloheximide-sensitive protein regulated by cyclic AMP is proposed to control cholesterol side-chain cleavage activity.
• A steroidogenesis activator polypeptide (SAP) was previously isolated and characterized from rat adrenocortical tissue.

Purpose of the Study:

• To purify and characterize SAP from rat H-540 Leydig cell tumors for amino acid sequencing.
• To synthesize and test the biological activity of a polypeptide based on the determined SAP sequence.

Main Methods:

• Purification of SAP from rat H-540 Leydig cell tumor.
• Amino acid sequencing of the purified SAP.
• Synthesis of a polypeptide based on the SAP sequence.
• Assay of cholesterol side-chain cleavage activity in adrenal mitochondria.

Main Results:

• A polypeptide activator of 30 amino acids and molecular weight 3215 was purified from rat H-540 Leydig cell tumor.
• The synthetic polypeptide demonstrated equipotent biological activity compared to native SAP in cholesterol side-chain cleavage assays.
• This suggests a potential role for SAP in regulating cholesterol metabolism in steroidogenic organs.

Conclusions:

• The study successfully purified and sequenced a key regulatory polypeptide (SAP) involved in steroidogenesis.
• The synthetic SAP confirmed its biological activity, validating the sequence and its role.
• Hormonal regulation of intracellular SAP concentration may be a critical mechanism controlling cholesterol metabolism in steroidogenic tissues.