general question about enzyme kinetic parameters kcat specific activity... - (Aug/20/2008 )
I'm collecting data on enzyme kinetic parameters for mathematical simulations and having a lot of trouble with kcat values. It appears that they are highly variable from one paper to another and that values for specific activity almost never translate into correct kcat values when you multiply with the molecular weight (KDa). Why so much variability? Am I doing something wrong? the specific activity in U/mg multiplied by the weight in KDa should give us the kcat in min-1. Isn't that correct? Even specific activities and kcat values from the same papers vary by about 30%. They vary by up to 10-fold between different papers.
are all the definitions of units the same? assay conditions (including incubation time)? enzyme source?
there are a lot of factors to take into consideration. the authors should tell you upon what they base their unit definition.
then you will need to normalize to make the comparisons.
tissues, the preparation of samples, and the conditions during measurements may vary; so all parameters of conditions must be mentioned; if the conditions between two studies, are not exactly the same, a comparison is only prelimenary...
but this is okay if you exactly describe what you have done;
even for, another example given, small-molecular chelators you will find various Ka and Kd values depending different conditions...