Association of some hydrolytic enzymes with the prostasome membrane and their differential responses to detergent and PIPLC treatment

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Abstract
Prostasomes are human prostate derived organelles that were isolated from both prostatic fluid and seminal plasma for the present study. Specific activities were determined for prostasome membrane‐associated enzymes, alkaline phosphatase (ALP), 5′‐nucleotidase (5′NT), and alkaline phosphodiesterase I (APD). The mode of their membranous anchoring was studied by treatment of prostasomes with phosphoinositol‐specific phospholipase C (PIPLC) and different detergents. A substantial amount of ALP (50%) and 5′NT (31%) was released by incubation of prostasomes with 2 U/ml of PIPLC contrary to the small amount of APD (12%) released by the same treatment. After PIPLC treatment, the enzymes were recovered in the aqueous phase after phase repartition in Triton X‐114 indicating that PIPLC removed the hydrophobic domain converting the enzymes from membrane‐linked to aqueous soluble forms. Octyl glycoside was the most efficient one among different detergents to solubilize the enzymes from the prostasome membrane. Both ALP and 5′NT were resistant to the treatment with Triton X‐100 and Triton X‐114. These results suggest that ALP, 5′NT, and APD are more or less extensively linked to the prostasome membrane via a glycophosphoinositide anchor.