Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.1 (phosphodiesterase)
 18,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Calmodulin (CaM) was purified from bovine brain and identified on the basis of its phosphodiesterase activity. Its purity was further tested by electrophoretic migration in polyacrylamide gels in the presence of sodium dodecyl sulfate. Apo-CaM was prepared from holo-CaM using hydroxyapatite chromatography. The Ca2+ binding sites on CaM and the pKa of each of the functional groups bound to Ca2+ were identified from the dependence of Ca2+ interaction with the functional group as a function of pH. EGTA was found to diminish the peaks corresponding to the pKa values of the groups bound to Ca2+. The use of bromophenacyl bromide, a modifier for aspartate and glutamate residues in proteins, diminished the peaks at pH = 3.4 and 4.3. Diethyl pyrocarbonate, a modifier for histidine residues, reduced the peak at pH = 6.2, corresponding to the pKa of the imidazole group in histidine. Furthermore, the peak at pH = 11.6 was eliminated using the specific tyrosine modifier, N-acetylimidazole. Diethylpyrocarbonate also eliminated four small peaks at pH = 7.2, 7.8, 8.2 and 8.8. This effect could be attributed to the binding of threonine and serine residues. The crystallographic results for parvalbumin, which has a similar molecular structure, suggest identical Ca2+ binding sites.
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PMID:Elucidation of pKa values for Ca2+ binding sites in calmodulin by spectrofluorometry. 784 65

Camp is a major regulator of platelet function. cGMP-inhibited phosphodiesterase (cGI-PDE) is the predominant platelet enzyme hydrolysing cAMP. The pH-rate profile plot for this enzyme yields pKa values of 6.5 and 9.0, consistent with histidine and cysteine residues respectively. Diethyl pyrocarbonate (DEP) inactivates cGI-PDE in a time- and concentration-dependent manner, and this effect was rapidly reversed by hydroxylamine. It was estimated that 2 mol of histidine residues per mol of enzyme were responsible for the loss of catalytic activity, as deduced from the correlation of the difference spectrum at 240 nm of the DEP-modified cGI-PDE with the enzyme activity. N-Ethylmaleimide (NEM) and 5.5'-dithiobis-(2-nitrobenzoic acid) (DTNB) inactivate cGI-PDE in a time- and concentration-dependent manner, suggesting the selective modification of a cysteine residue. AMP protects the enzyme against DEP, NEM and DTNB, suggesting the presence of histidine and cysteine residues at the active site of cGI-PDE. [14C]DEP incorporation in the presence of AMP or cGMP indicates the protection of two histidine residues by each nucleotide. These residues are different for each agent, since the combination of AMP and cGMP protects four histidine residues. [3H]NEM incorporation showed that 1 mol of cysteine per mol of cGI-PDE was protected by AMP, but not only by cGMP. We conclude that cGI-PDE possesses two essential histidine residues for activity, two additional histidines for cGMP inhibition, and one cysteine residue at the active site.
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PMID:Evidence for the presence of essential histidine and cysteine residues in platelet cGMP-inhibited phosphodiesterase. 871 77