Implications of the Alternating Access Model for Organic Anion Transporter Kinetics

Implications of the Alternating Access Model for Organic Anion Transporter Kinetics Many transport proteins, including the clinically important organic anion transporters (OATs), appear to function via an “alternating access” mechanism. In analyzing the kinetics of these transporters, the terms K m and V max are often treated in the field as denoting, respectively, the affinity of the substrate for the transporter and the turnover (conformational switch) rate of the substrate–transporter complex. In fact, the expressions for both these parameters have very complex forms comprising multiple rate constants from conformational switch as well as association/dissociation steps in the cycling of the transporter and, therefore, do not have straightforward physical meanings. However, if the rapid equilibrium assumption is made (namely, that the association/dissociation steps occur far more rapidly than the conformational switch steps), these expressions become greatly simplified and their physical meaning clear, though still distinct from the conventional interpretations. V max will be a function of not just the rate of substrate–transporter complex turnover but also the rate of the “return” conformational switch and will vary largely with the slower of these two steps (the rate-limiting step). K m will be seen to be related to substrate affinity by a term that varies inversely with the substrate–transporter complex turnover rate, essentially because the greater this rate, the greater the extent to which transporters will be distributed in a conformation inaccessible to substrate. Here, an intuitive approach is presented to demonstrate these conclusions. The phenomena of trans-stimulation and trans-inhibition are discussed in the context of this analysis. The Journal of Membrane Biology Springer Journals

Implications of the Alternating Access Model for Organic Anion Transporter Kinetics

Loading next page...
Copyright © 2008 by Springer Science+Business Media, LLC
Life Sciences; Human Physiology ; Biochemistry, general
Publisher site
See Article on Publisher Site


You’re reading a free preview. Subscribe to read the entire article.

DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 12 million articles from more than
10,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Unlimited reading

Read as many articles as you need. Full articles with original layout, charts and figures. Read online, from anywhere.

Stay up to date

Keep up with your field with Personalized Recommendations and Follow Journals to get automatic updates.

Organize your research

It’s easy to organize your research with our built-in tools.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

Monthly Plan

  • Read unlimited articles
  • Personalized recommendations
  • No expiration
  • Print 20 pages per month
  • 20% off on PDF purchases
  • Organize your research
  • Get updates on your journals and topic searches


Start Free Trial

14-day Free Trial

Best Deal — 39% off

Annual Plan

  • All the features of the Professional Plan, but for 39% off!
  • Billed annually
  • No expiration
  • For the normal price of 10 articles elsewhere, you get one full year of unlimited access to articles.



billed annually
Start Free Trial

14-day Free Trial