title: Sensitive assay detects protein methylesterase in spermatozoa: decrease in enzyme activity during epididymal maturation.
abstract: A more sensitive assay for protein methylesterase (PME) was developed. The new assay measures the methanol formed from hydrolysis of protein-methyl esters instead of methyl esters remaining on proteins. The formation of methanol is linear with time and enzyme concentration up to 20% of substrate hydrolysis. With this assay, we have detected very low PME activity in rat spermatozoa from cauda epididymidis. However, PME activity in spermatozoa from caput epididymidis was 10-fold higher. In a more detailed study on bull spermatozoa during epididymal maturation, we observed that PME activity was low in testicular spermatozoa, increased in spermatozoa from caput epididymidis to a maximum of 1.29 pmol/mg protein, and progressively decreased to a very low level (0.06 pmol/mg protein) in spermatozoa from cauda epididymidis. The drop in PME activity during epididymal transit parallels the progressive acquisition of motility and fertilizing capacity by spermatozoa.
mesh_terms: D000818:Animals; D002417:Cattle; D004822:Epididymis / Q000166:cytology*; D006868:Hydrolysis; D008297:Male; D000432:Methanol / Q000378:metabolism; D008722:Methods; D010047:Ovalbumin / Q000031:analogs & derivatives / Q000378:metabolism; D011496:Protein Methyltransferases / Q000378:metabolism*; D051381:Rats; D013079:Sperm Maturation; D013083:Sperm Transport; D013094:Spermatozoa / Q000201:enzymology*; D013737:Testis / Q000166:cytology
chemical_list: D010047:Ovalbumin; D011496:Protein Methyltransferases; D000432:Methanol