Purification and partial characterization of proteinase inhibitors of equine seminal plasma.

This research article explores and identifies proteinase inhibitors present in equine seminal fluid, their inhibitory potential, and their correlation with horse maturity based on protein concentration. The results point to older stallions having less total seminal plasma protein concentration, but similar levels of proteinase inhibitors. Various forms of these inhibitors might serve as potential unique biomarkers for individual stallions.

Objective of the Study

• The primary objectives of this study were threefold. Firstly, the researchers intended to isolate and identify proteinase inhibitors in equine seminal plasma – these are proteins that inhibit enzymes breaking down other proteins. Secondly, they wanted to ascertain the inhibitory potential of these proteinase inhibitors. Lastly, they aimed to discover a correlation between protein concentration in seminal plasma supernatant (obtained after precipitation with 36% ammonium sulfate) and a stallion’s sexual maturity.

Methodology

• Seminal plasma proteins were obtained from six different stallions as the sample for this experiment.
• These proteins were subjected to chromatography in a Superose 12 (FPLC system) column, which separates proteins based on their size, followed by a C(18) HPLC reverse-phase, a different type of chromatography that separates proteins based on their polarity.
• The inhibition of trypsin – an enzyme that breaks down proteins in the digestive system – amidase activity was examined within the collected fractions. This was to understand the inhibitory role of the identified proteinase inhibitors.

Findings

• Proteins that exhibited active inhibitory behavior, with a molecular mass ranging from 6.3 to 7.0 KDa, were identified using a technique called mass spectrometry. This tool allows for the analysis of the mass and structure of molecules.
• Older stallions had a reduced concentration of total protein in seminal plasma, but the concentrations of proteinase inhibitors remained the same (0.28+/-0.10 mg/ml) in the seminal plasma supernatant. This suggests that the proteinase inhibitor concentration is independent of the horse’s age or sexual maturity.
• Different isoforms – versions of the same protein that have slight structural differences – of proteinase inhibitors were found in the semen of all stallions, insinuating that these could be used as biomarkers to differentiate individual animals.