An Mn2+-stimulated neutral-sphingomyelinase in seminiferous tubules of immature Wistar rats

Mammalian sphingomyelinases have been implicated in many important physiological and pathophysiological processes. The seminiferous tubules of immature (19 day-old) Wistar rats have at least three types of sphingomyelinases, a lysosomal one and two microsomal ones. One of the microsomal sphingomyelinases is active at pH 6.5 and is stimulated by Mn²⁺ > Co²⁺ > Mg²⁺, and the other is active at pH 7.4 and is stimulated by Mn²⁺ > Mg²⁺ and inhibited by Co²⁺. The two microsomal enzymes are only slightly inhibited by EDTA and at pH 7.4 the stimulatory effects of Mn²⁺ and Mg²⁺ are additive. These data characterize the existence of two different membrane-bound sphingomyelinases in the seminiferous tubules of the rat.