Is it possible for a cell to have two or more isoenzymes catalyzing a biochemical reaction at the same time? For instance, we know that two alcohol dehydrogenase (ADH) isoenzymes simultaneously catalyze opposite reactions. However, is it possible for two isozymes to simultaneously catalyze a same reaction (not opposite directions)? Since the kinetic characteristics of these isoforms are different, can we assume that a particular biochemical reaction is catalyzed by multiple isoenzymes at the same time?
Thanks!
Yes, it is possible. For instance, hexokinases. During post-prandial period, hexokinase I and hexokinase IV are involved in the formation of Glucose-6-phosphate in hepatocytes. There are other examples.
Dear Francisco,
Thanks for your response. But, how we can justify the behavior of the cell in expression of two isozymes at the same time (of course fine-tuning is a good reason) when there exists other enzymes that have no isoform? In fact, is there any rational explanation that why some biochemical reactions can be catalyzed by multiple isozymes while others can't? Moreover, the expression level of these isozymes differ from one another, indicating one may catalyze that certain reaction more efficiently (not necessarily "better" in terms of kinetics); so, how we can justify this cellular behavior as well?
Thanks in advance.
Not an expert on Hexokinases but in general it's often about localization and evolution - certain enzymes are only needed at one place (cytoplasm or nucleoplasm or particular membranes or...) whereas others are needed in different places. to get there they can use different ways eg piggy back transport or if/when targeting motifs evolved into their primary sequences. this allows your enzyme to get into mitochondria / peroxisomes / certain vesicle families etc but also explains the emergence of different isozymes. hope this helps
Veerle,
Thanks for your response, it makes sense. So, can we call this behavior (catalyzing the same reaction at the same time) a cooperative function of these isozymes? However, this cannot be general, since as you've mentioned isoenzymes may be required in different organelles; but, how can we determine the biochemical "nature" of a reaction in this way? For instance, assume I've got a gene expression profile of a hypothetical cell indicating that genes encoding the isozymes of reactions namely R1 (containing two isozymes) and R2 (containing three isozymes) are highly regulated. Can we deduce that R1 and R2 are catalyzed by these isoenzymes "at the same time"? My point is that, is there any way to interpret such cellular behavior solely from expression profiles (or proteomics data) without any prior knowledge of protein localization?
Thanks in advance.
- Badges
- Science topic
- Similar topics
- Chemistry
- Biochemistry