Effect of tyrosine modification on the biological and immunological properties of equine chorionic gonadotropin.

The researchers have investigated how nitration–a chemical modification–of tyrosine, an amino acid, in equine chorionic gonadotropin, a horse hormone, affects its biological and immunological functions. They find that complete nitration diminishes the hormone’s activities, suggesting that tyrosine plays a crucial role in the functionality of this hormone.

Study Objective and Methodology

• The primary objective of this research was to understand the role of tyrosine residues in equine chorionic gonadotropin (eCG), a hormone affecting the reproductive system in horses.
• Researchers nitrated the tyrosine residues using a chemical compound called tetranitromethane. Nitration is a process that adds a nitro group to an organic compound, altering its properties.
• The degree of nitration was determined by the molar excess of tetranitromethane used, ranging from 100-fold molar excess to 8.6-fold in the presence of guanidine hydrochloride, a powerful protein denaturant.

Results

• The results showed that all tyrosine residues in eCG were affected by tetranitromethane under both conditions used.
• Complete nitration led to a complete loss of the hormone’s biological activity and a significant decrease in its immunological activity. The biological activities of a hormone refer to its functional roles in the body, while its immunological activities refer to its interaction with the immune system.
• The nitration of a single tyrosine resulted in a 70% reduction of the LH (luteinizing hormone) activity, which played a critical role in reproductive processes.
• Similarly, the FSH (follicle-stimulating hormone) activity followed a comparable reduction trend. FSH activity is also key in reproductive processes.
• Maximum nitration led to a 50% reduction in the immunological activity of the native hormone.
• Nitrated derivatives of the eCG were unable to compete with the native hormone in the rat Leydig cell assay for LH. The inability to compete indicates the reduced functional ability of the modified hormone.

Conclusion

• The findings clearly stress the importance of tyrosine residues in the functional manifestation of both FSH and LH activity in eCG.
• These results might have significant implications in the field of reproductive biology and potential impacts on the breeding and health of horses.