Abstract
(1) The time-course of inhibition by N- ethylmaleimide (NEM) of ( Na + + K +)- ATPase and K +-p- nitrophenylphosphatase activity of ( Na + + K +)- ATPase from Squalus acanthias has been followed over a 4000-fold inhibitor concentration range. The ( Na + + K +)- ATPase and the K +-p- nitrophenylphosphatase were inhibited in parallel at all inhibitor concentrations. (2) The data obtained have led to a model with the following features. (a) The enzyme is inactivated via two routes in which the reactivities towards NEM are different. This can explain that about 80% of the activity disappears 40–1000-times faster than the remaining 20%. (b) A primary reaction of SH groups with NEM without inhibition which is required before (c) a subsequent rection with NEM and inhibition can take place (i.e., a lag period). (d) A complicated concentration dependence of the rates of inactivation in the rapid phase which is interpreted in terms of an additional equilibrium between two different enzyme conformations. (3) The results are compatible with our previous finding (Esmann, M. (1982) Biochim. Biophys. Acta 688, 260–270) that more than one SH group per enzyme molecule are modified when the enzyme is inactivated.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Biochimica et Biophysica Acta (BBA) - Biomembranes
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
