BOVINE TESTIS AND HUMAN ERYTHROCYTES CONTAIN DIFFERENT SUBTYPES OF MEMBRANE-ASSOCIATED INS(1,4,5)P-3 INS(1,3,4,5)P-4 5-PHOSPHOMONOESTERASES/

1. We have purified membrane-associated Ins(1,4,5)P-3/Ins(1,3,4,5)P-4 5-phosphatases from bovine testis and human erythrocytes by chromatogr aphy on several media, including a novel 2,3-bisphosphoglycerate affin ity column. 2. The enzymes have apparent molecular masses of 42 kDa (t estis) and 70 kDa (erythrocyte), as determined by SDS/PAGE, and affini ties for Ins(1,4,5)P-3 of 14 mu M and 22 mu M respectively. 3. The two enzymes hydrolyse both Ins(1,4,5)P-3 and Ins(1,3,4,5)P-4 and are ther efore type I Ins(1,4,5)P-3 5-phosphatases [nomenclature of Hansen, Joh anson, Williamson and Williamson (1987) J. Biol. Chem. 262, 17319-1732 6]. 4. On chromatofocusing, the partially purified testicular enzyme m igrates as two peaks of activity, with pI values of about 5.8 and 5.5. The erythrocyte enzyme exhibits only the latter peak. 5. The testis 5 -phosphatase is labile at 37 degrees C, but its activity can be mainta ined in the presence of 50 mM phorbol dibutyrate (PdBu). After PdBu tr eatment, a third form of the enzyme, with pI about 6.2, appears on chr omatofocusing, but without change in its K-m or V-max. 6. Consideratio n of the properties of these enzymes and of the 5-phosphatases from ot her tissues suggests that type I Ins(1,4,5)P-3 5-phosphatases are of t wo well-defined subtypes. We propose that these be termed type Ia [typ ified by the testis enzyme: similar to 40 kDa, higher affinity for Ins (1,4,5)P-3] and Type Ib [typified by the erythrocyte enzyme: similar t o 70 kDa, lower affinity for Ins(1,4,5)P-3].