PubMed Health⌕ Search

Biomedical subjects

E T Rakitzis

Publications and source records attributed to E T Rakitzis.

48 records · Page 3Linked to original sources
PubMed1978

Kinetic analysis of the inhibition of sulfate transport in human red blood cells by isothiocyanates.

A kinetic analysis of anion self-exchange in human red blood cells, in the presence of an irreversible inhibitor, is presented and applied to the study of the inactivation of sulfate transport by three isothiocyanates: 3-isothiocyano-1,5-naphthalenedisulfonic acid, disodium salt (INDS), 1-isothiocyano-4-naphthalene sulfonic acid, sodium salt, monohydrate (INS), and 1-isothiocyano-4-benzenesulfonic acid, sodium salt, monohydrate (IBS). The time dependence of the inhibition of sulfate transport by the isothiocyanates used could be described by a single exponential and could be shown to contain a reversible and an irreversible component. In each case a portion of sulfate efflux was found to be resistant to inactivation. The residual portion of the sulfate efflux varied with inhibitor: 4% for INS, 16% for INDS, and 34% for IBS. INS showed the largest reversible inhibitory effect (12% of the flux remaining at 0.2 mM inhibitor concentration), while INDS showed the weakest effect (92% of the flux remaining at 0.3 mM inhibitor concentration). IBS had the highest rate of inactivation while INDS had the lowest. The kinetic analysis further suggests that all three isothiocyanates bind reversibly to an inhibitory site on the membrane before they bind covalently, and therefore irreversibly, to the same site on the membrane. The equilibrium constant for the dissociation of the reversibly-bound complex, Ki, and the rate of irreversible inactivation after all membrane sites are reversibly bound, kmax, have been computed for all three inhibitors: INDS (Ki = 420 micron, kmax = 5.04 hr-1), INS (Ki = 148 micron, kmax = 6.48 hr-1), and IBS (Ki = 208 micron, k(max) = 8.11 hr-1).

Biological Transport, Active↗
PubMed1976

Inactivation of cathepsin D by dithiophosgene and by 2,2-dichloro-1,3-dithiacyclobutanone.

Cathepsin D, purified from bovine spleen, is inactivated by the unstable inhibitors dithiophosgene and 2,2-dichloro-1,3-dithiacyclobutanone. Inhibition constants are identical for both of the compounds tested: Ki 96.1 muM;k/c0.406. It appears that the active species is 2,2-dichloro-1,3-dithiacyclobutanone, to which dithiophosgene is hydrolysed before cathepsin D inactivation.

Animals↗
PubMed1974

Kinetics of irreversible enzyme inhibition by an unstable inhibitor.

A mathematical treatment for the general case of enzyme inactivation by an inhibitor that breaks down in solution in a first-order reaction is presented. Cathepsin D was inactivated by fluorescein isothiocyanate with a K(i) of 4.47mum. Kinetic constants were also determined for the inactivation of cathepsin D by 1,1-bis(diazoacetyl)-2-phenylethane, and the inactivation of pepsin C by diazoacetyl-dl-norleucine methyl ester.

Cathepsins↗
PubMedDate not supplied

Inactivation of rhodanese from human gastric mucosa and stomach adenocarcinoma by 2,4, 6-trinitrobenzenesulphonate and by 4,4'-diisothiocyanatostilbene-2,2'-disulphonate.

Rhodanese (thiosulphate sulphurtransferase, EC 2.8.1.1) was partially purified from normal human gastric mucosa and from gastric adenocarcinoma by DEAE-cellulose column chromatography. Rhodanese inactivation by 2, 4, 6-trinitrobenzenesulphonate and by 4,4'-diisothiocynatostilbene-2-2'-disulphonate was studied by an analysis of the time-dependence of rhodanese activity loss. Rhodanese inactivation by 2, 4, 6-trinitrobenzenesulphonate was, under all conditions tested, found to be first-order with regard to enzyme residual activity. In contrast to this, rhodanese inactivation by 4, 4'-diisothiocyanatostilbene-2, 2'-disulphonate was found to be biphasic, when log residual enzyme activity was plotted vs reaction time. The first-order rate constant, k, for rhodanese inactivation by 2, 4, 6-trinitrobenzenesulphonate was, at all pH values tested, higher with the gastric adenocarcinoma enzyme than with the normal mucosa enzyme: at pH 8.00, k is 27.0 per hour, for the normal mucosa enzyme, while for the adenocarcinoma enzyme k is 69.0 per hour. In contrast to this, no difference in the inactivation profile of the normal mucosa enzyme and the gastric adenocarcinoma enzyme was to be observed with 4,4'-diisothiocyanatostilbene-2,2'-disulphonate.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗