title: [Aspartate aminotransferase from chicken heart cytosol. Characterization of SH-groups].
abstract: Homogeneous aspartate aminotransferase has been prepared from chicken heart cytosol. The purification procedure includes fractionation with NH4-sulfate and with ethanol, chromatography on ion-exchange cellulose DE-32 and on hydroxylapatite. Crystallization of the enyme is described. The enzyme was shown to contain 4 SH-groups per protein subunit of molecular weight 50 000. Two of the SH-groups are fully buried, they can be blocked with thiol reagents only upon denaturation of the protein. One exposed SH-group is readily modified at alkaline pH by iodoacetamide, N-ethymaleimide or tetranitromethane, without any inhibition of enzymic activity; this group readily reacts also with 5,5,-ditthiobis (2-nitrobenzoate) and p-mercuribenzoate. One SH-group is semi-buried: it is inaccessible to the above-mentioned reagents at pH 8, but can be blocked by p-mercuribenzoate at pH about 5. Blocking with p-mercuribenzoate of two SH-groups-the exposed and the semi-buried one-lowers enzymic activity to 70% of the initial value. Syncatalytic modication of a SH-group observed in aspartate aminotransferase from pig heart cytosol does not occur in chicken enzyme.
mesh_terms: D000818:Animals; D001219:Aspartate Aminotransferases / Q000032:analysis* / Q000037:antagonists & inhibitors; D002645:Chickens; D003600:Cytosol / Q000201:enzymology*; D008970:Molecular Weight; D009206:Myocardium / Q000201:enzymology*; D011489:Protein Denaturation; D013329:Structure-Activity Relationship; D013438:Sulfhydryl Compounds / Q000032:analysis*; D013439:Sulfhydryl Reagents / Q000494:pharmacology
chemical_list: D013438:Sulfhydryl Compounds; D013439:Sulfhydryl Reagents; D001219:Aspartate Aminotransferases
vernacular_title: Aspartat-transaminaza iz tsitoplazmy kur. Ochistka fermenta i issledovanie sul'fgidril'nykh grupp