J. Suarez et Vc. Desanchez, INHIBITION OF S-ADENOSYL-L-HOMOCYSTEINE HYDROLASE BY ADRENALINE IN ISOLATED GUINEA-PIG PAPILLARY-MUSCLES, International journal of biochemistry & cell biology, 29(11), 1997, pp. 1279-1284
Purified S-adenosyl-L-homocysteine hydrolase from Dictyostelium discoi
deum or rabbit erythrocytes is inactivated when incubated with cAMP, T
he aim of this study was to investigate whether adrenaline, which incr
eases cytosolic cAMP and calcium concentrations, is able to modify in
situ the activity of S-adenosyl-L-homocysteine hydrolase in the heart.
The enzyme was assayed in a crude extract obtained from superfused gu
inea-pig papillary muscles with the different tested substances. Adren
aline was found to inhibit S-adenosyl-L-homocysteine hydrolase in papi
llary muscles in a concentration-dependent fashion. This inhibition wa
s associated with an increase in the concentration of S-adenosyl-L-hom
ocysteine (326%), and a decrease of adenosine (40%), beta-Adrenoceptor
s are involved in the effect of adrenaline, since isoproterenol, a bet
a-adrenergic agonist, inhibited the enzyme, whereas the beta-adrenergi
c blocker, propranolol, prevented this inhibition, Participation of ca
lcium in the inhibitory effect of adrenaline was suggested because the
calcium channel blocker, verapamil, suppressed this inhibition, and h
igh calcium in the perfusion medium inhibited the enzyme. In vitro exp
eriments with calcium were performed in a semi-purified fraction of th
e enzyme, resulting in a concentration-dependent inhibition of the enz
yme, Calcium concentration, which inhibited the enzyme 50%, was in the
millimolar range for control and in the micromolar range for the obta
ined enzyme from adrenaline-treated muscles, indicating a different se
nsitivity to calcium inhibition, We conclude that adrenaline inhibits
S-adenosyl-L-homocysteine-hydrolase in situ, probably by a calcium-mod
ulated mechanism. (C) 1997 Published by Elsevier Science Ltd. All righ
ts reserved.