Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.5.4.4 (adenosine deaminase)
 5,136 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Dissociation constants (Kd) of ractopamine and clenbuterol for the swine adipocyte beta-adrenergic receptor were estimated from competition studies with epinephrine for the stimulation of lipolysis. Both compounds competitively inhibited epinephrine-stimulated lipolysis in the absence of adenosine deaminase. Three methods for estimating Kd values were used and similar estimates were obtained with each method. Ractopamine and clenbuterol showed greater affinity for the beta-receptor than did epinephrine and had similar Kd values of 1 to 2 x 10(-7) M. The low capacity of ractopamine and clenbuterol to stimulate lipolysis in vitro does not result from poor coupling to the beta-receptor. Ractopamine and clenbuterol may be considered partial agonists, possessing high affinity for the beta-adrenoceptor but exhibiting a relative ineffectiveness for adenylate cyclase activation.
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PMID:Determination of the affinity of ractopamine and clenbuterol for the beta-adrenoceptor of the porcine adipocyte. 257 69

In the present study S-adenosylhomocysteine (SAH) hydrolase from the bovine kidney has been purified to apparent homogeneity by standard chromatographic procedures. The purified enzyme was free from adenosine deaminase activity and showed a one-banded pattern in SDS-PAGE with a monomer molecular mass of 47,500. The molecular mass of the native enzyme estimated by gel filtration was about 190,000. The pI was 5.5. For hydrolysis of SAH we found a Km of 5.0 +/- 1.2 microM and a V of 0.25 mumol/min/mg. In the direction of synthesis the Km for adenosine was 5.6 microM and V 0.53 mumol/min/mg. The enzyme activity was inhibited in the presence of adenosine with a Ki = 3 microM. In a second set of experiments we determined the binding characteristics of [3H]-adenosine to purified enzyme. The enzyme bound [3H]-adenosine with three apparent affinities: Kd1 = 6.8 +/- 0.7 nM and Bmax1 = 0.24 +/- 0.04 nmol/mg protein; Kd2 = 387 +/- 41 nM and Bmax2 = 1.4 nmol/mg protein, and Kd3 = 7.05 +/- 0.9 microM and Bmax3 = 9 nmol/mg protein. Binding of 25 nM [3H]-adenosine obeyed a monophasic reaction with a k+1 value of 0.025 min/nM. Dissociation of [3H]-adenosine-SAH hydrolase complex was markedly temperature dependent. After a 240-min incubation at 0 degrees C only 5-10% and at 20 degrees C 75% were displaceable. A fraction of 25% bound [3H]-adenosine was not displaceable by unlabeled adenosine. Our data show that the renal SAH hydrolase exhibits similar enzyme kinetics as the well-characterized SAH hydrolase from liver. The amount of SAH hydrolase present in renal tissues (1.4 nmol/g wet weight) could account almost entirely for the binding of renal tissue adenosine. Finally, we report for the first time a high affinity binding site of SAH hydrolase for adenosine, which remains unexplained at present.
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PMID:S-adenosylhomocysteine-hydrolase from bovine kidney: enzymatic and binding properties. 887 89