Creatine kinase isoenzymes in spermatozoa

Area of Science:

• Biochemistry
• Spermatozoa research
• Cellular energy metabolism

Background:

• Creatine kinase (CK) plays a vital role in cellular energy metabolism by catalyzing the reversible transfer of a high-energy phosphate group between ATP and creatine.
• Understanding the localization and function of CK isoforms in spermatozoa is crucial for comprehending sperm energy dynamics and motility.

Purpose of the Study:

• To identify and localize creatine kinase (CK) isoforms and adenylate kinase in chicken and human spermatozoa.
• To investigate the role of CK and phosphoryl creatine (CP) in sperm motility.

Main Methods:

• Cellulose polyacetate electrophoresis and immunoblots were used to identify BB-CK and MiMi-CK isoforms.
• Indirect immunofluorescence staining and immunogold staining were employed to localize CK isoforms within spermatozoa.
• Metabolic blockers were used to assess the dependence of sperm motility on CK and CP.

Main Results:

• Two CK isoforms, BB-CK and mitochondrial-bound MiMi-CK, and adenylate kinase were identified in chicken and human spermatozoa.
• BB-CK was localized in the sperm tail, while MiMi-CK was found in the midpiece mitochondria.
• Human seminal plasma contained significant amounts of BB-CK, unlike chicken seminal plasma.
• Sperm motility was found to be dependent on CK and CP.

Conclusions:

• The distinct compartmentalization of CK isoforms in spermatozoa suggests a creatine phosphate (CP) shuttle system, analogous to that in muscle tissue.
• This CP shuttle system likely plays a critical role in providing energy for sperm motility.
• Further research into CK isoforms and the CP shuttle could offer insights into male infertility and potential therapeutic targets.