Kessin R H, Orlow S J, Shapiro R I, Franke J
Proc Natl Acad Sci U S A. 1979 Nov;76(11):5450-4. doi: 10.1073/pnas.76.11.5450.
The extracellular adenosine 3',5'-cyclic monophosphate phosphodiesterase (3',5'-cyclic-nucleotide 5'-nucleotidohydrolase, EC 3.1.4.17) produced by Dictyostelium discoideum has two kinetic forms. The free enzyme has a Km of approximately 10 microM. The second form is the result of a complex formed with a heat-stable inhibitor and has a Km in the millimolar range. Treating the enzyme-inhibitor complex with dithiothreitol stimulated enzyme activity 20- to 100-fold and changed in Km from millimolar to micromolar. Dithiothreitol inactivated the inhibitor. Reconstituting purified enzyme with excess inhibitor returned the Km to the millimolar range. Under conditions known to inhibit the production of extracellular inhibitor or in mutants that lack it, extracellular phosphodiesterase activity was already high and could not be increased by dithiothreitol. The phosphodiesterase and inhibitor sedimented at 6 S and 3 S, respectively; the enzyme-inhibitor complex sedimented at 6.7 S.
盘基网柄菌产生的细胞外腺苷3',5'-环磷酸二酯酶（3',5'-环核苷酸5'-核苷酸水解酶，EC 3.1.4.17）有两种动力学形式。游离酶的米氏常数约为10微摩尔。第二种形式是与一种热稳定抑制剂形成复合物的结果，其米氏常数在毫摩尔范围内。用二硫苏糖醇处理酶-抑制剂复合物可使酶活性提高20至100倍，并使米氏常数从毫摩尔变为微摩尔。二硫苏糖醇使抑制剂失活。用过量抑制剂重构纯化酶可使米氏常数回到毫摩尔范围。在已知抑制细胞外抑制剂产生的条件下或在缺乏该抑制剂的突变体中，细胞外磷酸二酯酶活性已经很高，且二硫苏糖醇不能使其增加。磷酸二酯酶和抑制剂分别在6S和3S沉降；酶-抑制剂复合物在6.7S沉降。
