Identification of the retinal cyclic GMP phosphodiesterase inhibitory gamma-subunit interaction sites on the catalytic alpha-subunit.

The presence of circulating inhibitors able to decrease the renal Na-K-adenosinetriphosphatase (ATPase) activity (natriuretic hormones) was postulated some 30 years ago. In the present work, the natriuretic inhibitor HgCl2 was selected as a model compound for the structural characterization of a possible natriuretic pathway for Na-K-ATPase modification. The structural effects of Na-K-ATPase inhibition by HgCl2 were assessed by trypsinolysis of the blocked enzyme in comparison with untreated preparations. The results show that inactivation of Na-K-ATPase by HgCl2 leads to the release of the alpha-subunit from the membrane preferentially in the E2 conformation but also in the E1 conformation. Apparently, HgCl2 weakens the membrane anchoring of the alpha-subunit, presumably by loosening the alpha-beta-subunit interaction. By this mechanism, the sensitivity of the Na-K-ATPase to extracellular drugs, hormones, and antibodies, as well as to intracellular proteases and other regulatory factors, could be altered.

Download Full-text

The effect of the γ-subunit of the cyclic GMP phosphodiesterase of bovine and frog (Rana catesbiana) retinal rod outer segments on the kinetic parameters of the enzyme

Biochemical Journal ◽

10.1042/bj2650655 ◽

1990 ◽

Vol 265 (3) ◽

pp. 655-658 ◽

Cited By ~ 22

Author(s):

M M Whalen ◽

M W Bitensky ◽

D J Takemoto

Keyword(s):

Catalytic Activity ◽

Cyclic Gmp ◽

Active Sites ◽

Outer Segment ◽

Maximal Activity ◽

Inhibitory Effect ◽

Gamma Subunit ◽

Rod Outer Segment ◽

Gamma Subunits ◽

Alpha Beta

Rod-outer-segment cyclic GMP phosphodiesterase (PDE) (subunit composition alpha beta gamma 2) contains catalytic activity in alpha beta. The gamma-subunits are inhibitors. Removal of the gamma-subunits increases Vmax. without affecting the Km. The inhibitory effect of a single gamma-subunit (alpha beta gamma) on the Vmax. of alpha beta is much greater in bovine than in frog (Rana catesbiana) PDE. Bovine PDE in the alpha beta gamma 2 state has a Vmax. that is 2.6 +/- 0.4% of the Vmax. of alpha beta. The removal of one gamma-subunit to give alpha beta gamma results in a Vmax. 5.2 +/- 1% of that for maximal activity. Frog alpha beta gamma 2 has a Vmax. 10.8 +/- 2%, and alpha beta gamma has a Vmax. 50 +/- 18%, of the Vmax. of alpha beta. These data suggest that a single gamma-subunit can inhibit the catalytic activity of active sites on both alpha- and beta-subunits in bovine, but not in frog, rod-outer-segment PDE.

Download Full-text

Oocyte maturation in starfish is mediated by the beta gamma-subunit complex of a G-protein.

The Journal of Cell Biology ◽

10.1083/jcb.121.4.775 ◽

1993 ◽

Vol 121 (4) ◽

pp. 775-783 ◽

Cited By ~ 68

Author(s):

L A Jaffe ◽

C J Gallo ◽

R H Lee ◽

Y K Ho ◽

T L Jones

Keyword(s):

G Protein ◽

G Proteins ◽

Oocyte Maturation ◽

Alpha Subunit ◽

Meiotic Maturation ◽

Amino Terminus ◽

Hormone Response ◽

Gamma Subunit ◽

Gamma Subunits ◽

Stimulation Of

The stimulation of meiotic maturation of starfish oocytes by the hormone 1-methyladenine is mimicked by injection of beta gamma subunits of G-proteins from either retina or brain. Conversely, the hormone response is inhibited by injection of the GDP-bound forms of alpha i1 or alpha t subunits, or by injection of phosducin; all of these proteins should bind free beta gamma. alpha-subunit forms with reduced affinity for beta gamma (alpha i1 or alpha t bound to hydrolysis-resistant GTP analogs, or alpha i1-GMPPCP treated with trypsin to remove the amino terminus of the protein) are less effective inhibitors of 1-methyladenine action. These results indicate that the beta gamma subunit of a G-protein mediates 1-methyladenine stimulation of oocyte maturation.

Download Full-text