Major 56,000-dalton, soluble phosphoprotein present in bovine sperm is the regulatory subunit of a type II cAMP-dependent protein kinase
✍ Scribed by Marie-Christine Paupard; Janet MacLeod; Wilma Wasco; George A. Orr
- Publisher
- John Wiley and Sons
- Year
- 1988
- Tongue
- English
- Weight
- 862 KB
- Volume
- 37
- Category
- Article
- ISSN
- 0730-2312
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✦ Synopsis
It has been shown that CAMP-dependent phosphorylation of a soluble sperm protein is important for the initiation of flagellar motion. The suggestion has been made that this motility initiation protein, named axokinin, is the major 56,000-dalton phosphoprotein present in both dog sperm and in other cells containing axokinin-like activity. Since the regulatory subunit of a type II CAMP-dependent protein kinase is a ubiquitous CAMP-dependent phosphoprotein of similar subunit molecular weight as reported for axokinin, we have addressed the question of how many soluble 56,000-dalton CAMP-dependent phosphoproteins are present in mammalian sperm. We report that in bovine sperm cytosol, the ratio of the type I to type I1 CAMPdependent protein lunase is approximately 1 : 1. The type I1 regulatory subunit is related to the non-neural form of the enzyme and undergoes a phosphorylationdependent electrophoretic mobility shift. The apparent subunit molecular weights of the phospho and dephospho forms are 56,000 and 54,000 daltons, respectively. When bovine sperm cytosol or detergent extracts are phosphorylated in the presence of catalytic subunits, two major proteins are phosphorylated and have subunit molecular weights of 56,000 and 40,000 daltons. If, however, the type 11 regulatory subunit (RII) is quantitatively removed from these extracts using either immobilized CAMP or an anti-MI monoclonal affinity column, the ability to phosphorylate the 56,000but not 40,000-dalton polypeptide is lost. These data suggest that the major 56,000 dalton CAMP-dependent phosphoprotein present in bovine sperm is the regulatory subunit of a type I1 CAMP-dependent protein kmase and not the motility initiator protein, axokinin.