Effect of liver plasma membranes on G-actin. I. Possible implication of membrane NPases in inactivation of G-actin

Abstract

G-actin incubated in the presence of a liver fraction enriched in plasma membranes is rapidly inactivated, as indicated by the biphasic loss of polymerizability and DNase inhibition. The rates of inactivation as measured by viscosity are greatly influenced by temperature, but almost independent of membrane concentrations at least in the low range of concentrations tested (less than 250 micrograms protein/ml). The loss of DNase inhibition capacity proceeds at rates two to three times slower than the loss of polimerizability. The inactivation of actin in the presence of membranes cannot be attributed to proteolysis nor to a phosphorylation of actin by membranes. However, it is shown that in the course of the incubation, medium ATP is rapidly converted into AMP and adenosine and that the destruction of ATP is almost complete at the start of the inactivation process. A mechanism is presented relating the destruction of ATP to actin inactivation.

The membrane topography of ecto-5′-nucleotidase in rat hepatocytes

“…We have found that the effects of 5'-nucleotidase on actin inhibition ofdeoxyribonuclease are due to contaminating ATPases, which has also been shown for chick gizzard 5'-nucleotidase . The ability of actin to inhibit deoxyribonucleotidase I is lost on incubation at 37°C in the absence of ATP (results not shown), an effect that appears to be speeded up by the presence ofATPases (Gruda et al, 1983) and to be related to loss ofactin-bound nucleotide . The interaction with F-actin proposed for this chick gizzard 5'-nucleotidase, associated with enzyme inhibition, does not occur with pure rat liver 5'-nucleotidase.…”

Effect of liver plasma membranes on G-actin. II. Fate of actin-bound nucleotide

“…G-actin was prepared from acetone powder of rabbit skeletal muscles and a plasma-membrane-enriched preparation from rabbit liver as described elsewhere (1).…”