Proteinase inhibitors of horse seminal plasma. A high molecular mass, acid-soluble proteinase inhibitor.

This research article focuses on the identification and analysis of a protein complex in horse seminal plasma that acts as a proteinase inhibitor. Interestingly, this complex does not correspond to the equivalent inhibitor identified in human seminal plasma.

Key Findings

• The research identifies the presence of a high relative molecular mass proteinase inhibitor within horse seminal plasma. Unlike in humans, the horse seminal plasma does not contain a proteinase inhibitor equivalent to human HUSI-I.
• Named the Horse Seminal Plasma Protein Complex (HSPC), this component has a broad range of enzyme-inhibiting abilities. Its relative molecular mass is approximately 800,000.
• The HSPC is composed of seven different polypeptides with relative molecular mass values that range between 11,000 and 30,000. Further, it is found to contain between 3.5% and 5% carbohydrate content.
• Despite its high molecular mass, the HSPC is soluble even in dilute perchloric acid, and its inhibitory activities remain unaffected. The substantial recovery (69%) of seminal plasma protein after perchloric acid treatment suggests that HSPC is a significant component of horse seminal plasma.

Additional Observations

• Apart from the HSPC, the horse seminal plasma was found to contain another group of three distinct proteinase inhibitors. These demonstrated a relative molecular mass roughly around 6,500 and were only able to inhibit trypsin.
• The similar molecular mass and identical enzyme specificity of these inhibitors suggest that they might be isoinhibitors and could potentially be analogous to human HUSI-II.
• The absence of a human HUSI-I equivalent in horse seminal plasma is discussed in the research. This observation is compared with a previous finding that horse tracheobronchial fluid contains no identifiable proteinase inhibitors soluble in perchloric acid.