LIVER 3' - 5'-NUCLEOTIDE PHOSPHODIESTERASE AND ITS ACTIVITY IN RAT LIVERS PERFUSED WITH INSULIN

Most (80–90%) of the cyclic 3′:5′‐nucleotide phosphodiesterase activity in 0.25 M sucrose homogenates of rat liver was found in the 100,000 ×g× 30 min supernatant. The non‐particulate nature of the liver phosphodiesterase activity was also confirmed with beef and human liver. The phosphodiesterase activity of rat liver supernatant showed a pH maximum in the region of 7.0–7.5 in Tris‐Cl or cacodylate buffer, with a Km of 62 μM in Tris‐Cl buffer. A dependency on added Mg++ was indicated for maximum phosphodiesterase activity in rat liver supernatant. High‐speed centrifugation and Sephadex G‐200 chromatography studies indicated that phosphodiesterase activity is associated with a protein of high molecular weight (>200,000). Cyclic 3′:5′‐nucleotides with a purine base were preferentially hydrolyzed in all fractions of rat liver. Dibutyryl adenosine 3′:5′‐monophosphate exhibited complete resistance to rat liver phosphodiesterase hydrolysis in the two assay systems employed. The role of liver phosphodiesterase activity as a regulatory enzyme of adenosine 3′:5′‐monophosphate concentration in the action of insulin on liver was also investigated. Neither prior treatment of perfused livers with insulin nor presence of insulin in two different assay systems affected the phosphodiesterase activity in high‐speed supernatants. Copyright © 1969, Wiley Blackwell. All rights reserved