Discrimination of two functions of photoreceptor cGMP phosphodiesterase gamma subunit.
cGMP phosphodiesterase, a key enzyme in phototransduction, is composed of P alpha beta and two P gamma S. P gamma has two functions in P alpha beta regulation: (I) an inhibitor of cGMP hydrolysis and (II) a stimulator of cGMP binding to their noncatalytic sites. Here we show for the first time that these functions can be discriminated. P gamma release by GTP-bound transducing from P alpha beta was stimulated by NaCl in a concentration-dependent manner. However, phosphodiesterase activity in membranes washed with NaCl-free buffer already reached the maximum level. [3H]-cGMP binding of P alpha beta in membranes washed with NaCl required more P gamma than that in membranes washed without NaCl. Other salts had a similar effect. Identical P gamma was released under different [NaCl]. These results indicate that P gamma for the function (I) is released in low [salt], but P gamma for the function (II) is released in high [salt]. These P gamma functions may be expressed separately in phototransduction.
Yamazaki
A
A
Department of Opthalmology, Kresge Eye Institute, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
Yamazaki
M
M
Bondarenko
V A
VA
Matsumoto
H
H
D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000201:enzymology; D006152:Cyclic GMP / Q000378:metabolism; D003624:Darkness; D004789:Enzyme Activation; D006160:Guanosine Triphosphate / Q000378:metabolism; D006868:Hydrolysis; D007700:Kinetics; D046911:Macromolecular Substances; D013058:Mass Spectrometry; D008970:Molecular Weight; D011892:Rana catesbeiana; D011994:Recombinant Proteins / Q000378:metabolism; D012374:Rod Cell Outer Segment / Q000201:enzymology*; D012965:Sodium Chloride / Q000494:pharmacology; D014316:Tritium
D046911:Macromolecular Substances; D011994:Recombinant Proteins; D014316:Tritium; D012965:Sodium Chloride; D006160:Guanosine Triphosphate; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D006152:Cyclic GMP