Inhibition of lactate production in rat brain extracts and synaptosomes by 3-[4-(reduced 3-pyridine aldehyde-adenine dinucleotide)]-pyruvate

Cardioprotective activity of a novel and potent competitive inhibitor of lactate dehydrogenase

Alkaline incubation of NADH results in the formation of a very potent inhibitor of lactate dehydrogenase. High resolution mass spectroscopy along with NMR characterization clearly showed that the inhibitor is derived from attachment of a glycolic acid moiety to the 4-position of the dihydronicotinamide ring of NADH. The very potent inhibitor is competitive with respect to NADH. The inhibitor added in submicromolar concentrations to cardiomyocytes protects them from damage caused by hypoxia/reoxygenation stress. In isolated mouse hearts, addition of the inhibitor results in a substantial reduction of myocardial infarct size caused by global ischemia/reperfusion injury.

Characterization and histopathological correlation of cytosol proteins of benign and malignant breast tumors

Significant differences in cytosol protein level exist between normal/benign and cancerous breast tissues. There is a positive correlation between the cytosol protein level and histological grade of carcinoma. Well-differentiated carcinoma have a lower value of cytosol protein than poorly differentiated carcinoma. In slab gel electrophoregrams, the total numbers of bands are almost identical in normal, benign, and malignant conditions. In addition, 37 Kd protein band is consistently present in malignant cases and always absent in normal or benign cases. More extensive biophysical examination of this band may provide further insight into the protein alterations in cancer cells at the molecular level.

Inhibition of the bovine branched-chain 2-oxo acid dehydrogenase complex and its kinase by arylidenepyruvates

A novel class of inhibitors for the branched-chain 2-oxo acid dehydrogenase (BCOAD) complex has been synthesized and studied. The sodium salts of arylidenepyruvates: e.g., furfurylidenepyruvate (compound I), 4-(3-thienyl)-2-oxo-3-butenoate (compound II), cinnamalpyruvate (compound III) and 4-(2-thienyl)-2-oxo-3-butenoate (compound IV) inhibit the overall and kinase reactions of the BCOAD complex from bovine liver. Inhibitions of the overall reaction occur at the decarboxylase (E1) step as determined by a spectrophotometric assay with 2,6-dichlorophenolindophenol as an electron acceptor. Inhibition of the E1 reaction by compound I (Ki = 0.5 microM) is competitive, whereas inhibitions by compounds II (Ki = 150 microM) and III (Ki = 500 microM) are non-competitive with respect to the substrate 2-oxoisovalerate. The Km value for 2-oxoisovalerate is 6.7 microM as measured by the E1 assay. Inhibition of the E1 step by compounds I, II and III are reversible at low inhibitor concentrations based on the Michaelis-Menten kinetics observed. By comparison, compound I does not significantly inhibit pyruvate and 2-oxoglutarate dehydrogenase complexes. The arylidenepyruvates (compounds I, II and IV) inhibit the BCOAD kinase reaction in a manner similar to the substrate 2-oxo acids. The inhibition of the kinase reaction by compound I is non-competitive with respect to ATP, with an apparent Ki value of 4.5 mM. The results suggest that arylidenepyruvates may be useful probes for elucidating the reaction mechanisms of the BCOAD complex and its kinase.

Conversion of canavanine to alpha-keto-gamma-guanidinooxybutyrate and to vinylglyoxylate and 2-hydroxyguanidine

It was observed previously that hydroxyguanidine is formed in the reaction of canavanine(2-amino-4-guanidinooxybutanoate) with amino acid oxidases. The present work shows that hydroxyguanidine is formed by a nonenzymatic beta,gamma-elimination reaction following enzymatic oxidation at the alpha-C and that the abstraction of the beta-H is general-base catalyzed. The elimination reaction requires the presence in the alpha-position of an anion-stabilizing group--the protonated imino group (iminium ion group) or the carbonyl group. The iminium ion group is more activating than the carbonyl group. Elimination is further facilitated by protonation of the guanidinooxy group. The other product formed in the elimination reaction was identified as vinylglyoxylate (2-oxo-3-butenoate), a very highly electrophilic substance. The product resulting from hydrolysis following oxidation was identified as alpha-keto-gamma-guanidinooxybutyrate (ketocanavanine). The ratio of hydroxyguanidine to ketocanavanine depended upon the concentration and degree of basicity of the basic catalyst and on pH. In the presence of semicarbazide, the elimination reaction was prevented because the imino group in the semicarbazone derivative of ketocanavanine is not significantly protonated. Incubation of canavanine with 5'-deoxypyridoxal also yielded hydroxyguanidine. Since the elimination reactions take place under mild conditions, they may occur in vivo following oxidation at the alpha-C of L-canavanine (ingested or formed endogenously) or of other amino acids with a good leaving group in the gamma-position (e.g., S-adenosylmethionine, methionine sulfoximine, homocyst(e)ine, or cysteine-homocysteine mixed disulfide) by an L-amino acid oxidase, a transaminase, or a dehydrogenase. Therefore, vinylglyoxylate may be a normal metabolite in mammals which at elevated concentrations may contribute to the in vivo toxicity of canavanine and of some of the other above-mentioned amino acids.