IS CYSTEINE RESIDUE IMPORTANT IN FITC-SENSITIVE ATP-BINDING SITE OF P-TYPE ATPASES - A COMMENTARY TO THE STATE-OF-THE-ART

Treatment of P-type ATPases (from mammalian sources) by fluorescein is othiocyanate (ITC) revealed the ITC label on a lysine residue that was than considered as essential for binding of ATP in the ATP-binding si re of these enzymes. On the other hand, experiments with site directed mutagenesis excluded the presence of an essential lysine residue that would be localized in the ATP binding sites of ATPases. Other previou s studies, including those of ourselves, indicated that the primary si te of isothiocyanate interaction may be the sulflhydryl group of a cys teine residue and this may be essential for binding of ATP. In additio n considerable knowledge accumulated since yet also about the differen ces in stability of reaction product of isothiocyanates with SH- or NH 2-groups. Based upon evaluation of the data available up to now, in pr esent paper the following tentative roles for lysine and cysteine resi dues located in the ATP-binding site of P-type ATPases are proposed: T he positively charged micro-domain of the lysine residue may probably attract the negatively charged phosphate moiety of the ATP molecule wh ereas the cysteine residue may probably be responsible for recognition and binding of ATP by creation of a proton bridge with the amino grou p in position 6 on the adenosine ring of ATP.