Document Detail

Mechanism of sodium nitroprusside-mediated inhibition of aromatic amino acid decarboxylase activity.
MedLine Citation:
PMID:  7716178     Owner:  NLM     Status:  MEDLINE    
The effects of sodium nitroprusside (SNP) on dopamine synthesis in a porcine renal epithelial cell line (LLC-PK1) were evaluated. Subsequent studies examined the actions of the degradation products of SNP (cyanide, ferrous ion and nitric oxide) on aromatic amino acid decarboxylase (AAAD) activity in tissue supernatants from LLC-PK1 cells and rat renal cortex. SNP (10-500 mumol/l) significantly inhibited dopamine production in LLC-PK1 cells in a dose-related manner. The activation of guanylate cyclase by nitric oxide was not found to be the mechanism whereby SNP inhibited dopamine synthesis in LLC-PK1 nor did the antioxidant glutathione attenuate the actions of SNP. Ferrous sulfate (0.5 mmol/l) and SNP (0.5 mmol/l) were found to inhibit dopamine synthesis in LLC-PK1 cells and to directly inhibit cytosolic AAAD activity from LLC-PK1 cells. A series of studies were conducted using AAAD from rat renal cortex and confirmed that SNP could directly inhibit the conversion of L-dopa to dopamine by AAAD. Furthermore, potassium ferricyanide (1 mmol/l) and potassium cyanide (1 mmol/l) could produce greater than 80% reductions in AAAD activity. Iron (0.5-1 mmol/l) was found to increase rat kidney AAAD activity. Kinetic analysis revealed that potassium cyanide was a potent (Ki = 40-50 mumol/l) noncompetitive/mixed noncompetitive inhibitor of AAAD. SNP was also found to be a noncompetitive inhibitor of AAAD with a Ki of approximately 300-500 mumol/l. In contrast, ferrous sulfate (0.5 mmol/l) was a competitive inhibitor (Ki = approximately 650 mumol/l) that actually increased the Vmax of AAAD. The results of these studies support that cyanide released from SNP can potently inhibit AAAD, although SNP has somewhat more complex interactions with AAAD due to the presence of ferrous ion.
R Dawson; R Felheim; S Nguyen
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Publication Detail:
Type:  In Vitro; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Pharmacology     Volume:  50     ISSN:  0031-7012     ISO Abbreviation:  Pharmacology     Publication Date:  1995 Feb 
Date Detail:
Created Date:  1995-05-16     Completed Date:  1995-05-16     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0152016     Medline TA:  Pharmacology     Country:  SWITZERLAND    
Other Details:
Languages:  eng     Pagination:  74-85     Citation Subset:  IM    
Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville 32610, USA.
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MeSH Terms
Aromatic-L-Amino-Acid Decarboxylases / antagonists & inhibitors*
Cells, Cultured / metabolism
Cyclic GMP / analogs & derivatives
Deferoxamine / pharmacology
Dopamine / biosynthesis*
Ferrous Compounds / pharmacology
Glutathione / pharmacology
Kidney / drug effects,  metabolism*
Nitroprusside / pharmacology*
Potassium Cyanide / pharmacology
Pyridoxal Phosphate / pharmacology
Reg. No./Substance:
0/Ferrous Compounds; 15078-28-1/Nitroprusside; 151-50-8/Potassium Cyanide; 54-47-7/Pyridoxal Phosphate; 70-18-8/Glutathione; 70-51-9/Deferoxamine; 7665-99-8/Cyclic GMP; EC Decarboxylases

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