Hur K C, Louis C F
Department of Veterinary Biology, University of Minnesota, St. Paul 55108.
Biochim Biophys Acta. 1989 Jan 17;1010(1):56-63. doi: 10.1016/0167-4889(89)90184-5.
Localization of adenylate cyclase activity in the outer cortical regions of the bovine lens correlates with the restriction of the Gs and Gi guanine nucleotide regulatory subunits of this enzyme to these same regions of the lens. In contrast, the major membrane substrates for cAMP-dependent protein kinase (cAMP-PK) (molecular masses of 18, 26 and 28 kDa) were identified in both the inner nuclear and the outer cortical regions of the lens. However, there were differences in the relative amounts of Pi incorporated into the 18 kDa and 28 kDa components in different lens regions. The three major membrane substrates for cAMP-PK were also phosphorylated when homogenates of lens cortex were incubated with [gamma-32P]ATP plus activators of the lens adenylate cyclase. In contrast, there was no incorporation of 32P into these substrates when homogenates of lens nucleus were used. When exogenous cAMP was added to homogenates of lens nucleus or cortex, 32P was incorporated into the membrane substrates for cAMP-PK in both regions of the lens, indicating that cAMP-PK was present in both regions. Interestingly, cAMP phosphodiesterase activity was at least 10-times greater in lens cortex than in the lens nucleus. These results indicate that while the major membrane substrates for cAMP-PK could be phosphorylated in all regions of the lens, there is a restriction of those enzymes that synthesize and degrade cAMP to the outer cortical regions of this organ.
牛晶状体外部皮质区域中腺苷酸环化酶活性的定位与该酶的Gs和Gi鸟嘌呤核苷酸调节亚基在晶状体相同区域的分布局限相关。相比之下，在晶状体的内核区域和外部皮质区域均鉴定出了环磷酸腺苷依赖性蛋白激酶（cAMP-PK）的主要膜底物（分子量分别为18 kDa、26 kDa和28 kDa）。然而，不同晶状体区域中掺入18 kDa和28 kDa组分的磷酸根离子（Pi）的相对量存在差异。当将晶状体皮质匀浆与[γ-32P]ATP及晶状体腺苷酸环化酶激活剂一起孵育时，cAMP-PK的三种主要膜底物也会发生磷酸化。相反，使用晶状体核匀浆时，这些底物中没有32P掺入。当向晶状体核或皮质的匀浆中添加外源性cAMP时，晶状体两个区域中cAMP-PK的膜底物均有32P掺入，表明两个区域均存在cAMP-PK。有趣的是，晶状体皮质中的环磷酸腺苷磷酸二酯酶活性至少比晶状体核中的高10倍。这些结果表明，虽然cAMP-PK的主要膜底物在晶状体的所有区域均可被磷酸化，但合成和降解cAMP的酶局限于该器官的外部皮质区域。
