Open AccessThe phospho enol pyruvate‐dependent fructose‐specific phosphotransferase system in Rhodopseudomonas sphaeroides
Author(s) -
LOLKEMA Juke S.,
HOEVEDUURKENS Ria H.,
ROBILLARD George T.
Publication year - 1986
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1986.tb09447.x
Subject(s) - chemistry , dithiol , enzyme , biochemistry , dithiothreitol , phosphotransferase , substrate (aquarium) , trypsin , rhodospirillaceae , stereochemistry , biology , ecology
Two interrelated sites have been detected on the fructose carrier in Rhodopseudomonas sphaeroides : an activity‐linked dithiol and a Zn 2+ ‐binding site. Binding of Zn 2+ brings E Fru II into a new conformation that to some extent mimics the conformation of phosphorylated E Fru II , an essential intermediate in the turnover of the enzyme. Binding of zinc to E Fru II or phosphorylating the enzyme protects it against trypsin inactivation relative to the dephos‐phorylated zinc‐free enzyme. A dithiol is essential for activity. Interchanges between the redox states of the enzyme can be brought about by dithiothreitol and ferricyanide, but not, or very slowly, by molecular oxygen. The dithiol is protected, in the E Fru II ‐Zn 2+ complex, against (a) alkylation by MalNEt, (b) reversible oxidation by Fe(CN) 3‐ 6 and Cu 2+ , (c) irreversible oxidation by Cu 2+ . The p K value of the activity linked thiol is 7.8. Protection experiments show that the dithiol is not located in any of the substrate‐binding sites. The redox state of the enzyme does not influence the rate of inactivation of E Fru II by trypsin.