RESEARCH ARTICLE


Comparison of Two Measures of Missing Cofactor in Cofactor-Dependent Enzymes: Proportion Versus Relative Increase



Tomas Hansson*
Department of Applied Environmental Science (ITM), Stockholm University, SE-10691 Stockholm, Sweden


© 2012 Tomas Hansson

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Department of Applied Envi-ronmental Science (ITM), Stockholm University, SE-10691 Stockholm, Sweden; Tel: +46-8-6747368; Fax: +46-8-6747638; Email: tomas.hansson@itm.su.se


Abstract

The degree of missing cofactor in a cofactor-dependent enzyme is widely used as a biomarker of cofactor defi-ciency. The degree of missing cofactor can be expressed either as the proportion of enzyme without cofactor, or as the rel-ative increase in enzyme with cofactor after addition of excess cofactor to the sample. Especially for enzymes with thia-mine pyrophosphate (TPP) as a cofactor, the relative increase (TPP-effect) has been used in a majority of studies, and its use seems to prevail without consideration of the proportion (latency) as a better alternative. In this letter, the statistical properties of the two measures are compared in the context of a thiamine-dependent enzyme. Proportion is a more bal-anced and sensitive measure than relative increase, and simulation shows that proportion is associated with equal or high-er statistical power than relative increase. The power difference can be as high as 0.12.

Keywords: Cofactor, Enzyme, Latency, Statistical power, TPP-effect.