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B Pensa

Publications and source records attributed to B Pensa.

24 records · Page 2Linked to original sources
PubMed1975

Inactivation of rhodanese by pyridoxal 5'-phosphate.

Pyridoxal 5'-phosphate and other aromatic aldehydes inactivate rhodanese. The inactivation reaches higher extents if the enzyme is in the sulfur-free form. The identification of the reactive residue as an amino group has been made by spectrophotometric determination of the 5'-phosphorylated pyridoxyl derivative of the enzyme. The inactivation increases with pyridoxal 5'-phosphate concentration and can be partially removed by adding thiosulfate or valine. Prolonged dialysis against phosphate buffer also leads to the enzyme reactivation. The absorption spectra of the pyridoxal phosphate - rhodanese complex show a peak at 410 nm related to the Schiff base and a shoulder in the 330 nm region which is probably due to the reaction between pyridoxal 5'-phosphate and both the amino and thiol groups of the enzyme that appear reasonably close to each other. The relationship betweenloss of activity and pyridoxal 5'-phosphate binding to the enzyme shows that complete inactivation is achieved when four lysyl residues are linked to pyridoxal 5'-phosphate.

Animals↗
PubMed1975

Selenium binding to beef-kidney rhodanese.

The reaction of beef kidney rhodanese with selenosulfate was studied. The selenium-treated enzyme shows an absorption spectrum with a maximum at 375 nm attributable to a sulfoselenide group. This absorption is bleached by addition of cyanide. After cyanide treatment stoichiometric amount of selenocyanate can be found. The intrinsic fluorescence of rhodanese is quenched by addition of stoichiometric selenosulfate. This effect can be reversed by cyanide or sulfite but not by selenite or glutathione. By comparison with model complexes the selenium-rhodanese intermediate was identified as a cysteinyl-selenium derivative.

Animals↗
PubMedDate not supplied

Studies of cyanolysis of the rhodanese-thionitrobenzoate complex.

The reaction of sulfur-free rhodanese with 5-5'-dithio-bis (2-nitrobenzoic acid) produces a modified enzyme with 35% of residual activity. The resulting enzyme derivative has 1.6 moles of thionitrobenzoate/mole of enzyme bound to sulfhydryl groups of rhodanese. Determination of free sulfhydryl groups of this derivative shows that during the reaction with 5-5'-dithio-bis (2-nitrobenzoic acid) oxidative formation of an intramolecular disulfide bridge between two sulfhydryl groups of rhodanese occurs. Cyanolysis of the modified enzyme produces an enzyme-thiocyano derivative which partially beta-eliminates with release of thiocyanate. The cleavage of disulfide bonds present in the enzyme-thionitrobenzoate adduct using labeled cyanide shows an incorporation of radioactivity in the protein higher than would be expected. An electrostatic bond between cyanide and positively charged groups of the enzyme is suggested. Most of bound cyanide is released when samples are acidified for protein hydrolysis. In these conditions the thiocyanoalanine residue cyclizes to form 2-iminothiazolidine-4-carboxylic acid.

Animals↗