Some part of the microbial enzymes are released from the cell but a huge portion of the enzymes remain inside the cell and with time released gradually or that can be extracted by grinding their cells instantly. But when same amount of enzymes (same enzyme unit) released from the cell (extra-cellular) and grinding to the cell (intra-cellular) are compared it has been found that extra-cellular enzymes are at-least 25-30% more efficient in hydrolyzing (breaking down) the substrate than their intra-cellular counterpart. What are the possible reasons behind it?
Hello Sir.
It is a nice question. If I am right the more efficiency of the extracellular enzymes than intracellular is just because of the process of extraction. As we know the extraction process is also an important factor for the stability of any enzymes. During intracellular enzymes extarction may be the enzymes loose some potentiality for hydrolyzation.
If you are saying both have same enzyme unit then I don't think they will show any differences in hydrolyzation. Eagerly waiting if any one contribute the reason behind this.
-AKM
Hi there,
Are the secreted and cellular forms of enzymes you are writing about encoded by the same gene or by different genes? If the latter the proteins may not be strictly identical in sequence which might account for different catalytic properties. If the former then the different forms of the same enzyme are basically identical so there is no obvious reason why they should exhibit different activities in a formated assay. Then the different extraction protocols used might explain the difference concerning the activity of the enzyme (a treatment made to release a cellular protein is always harsher than a treatment with the view to collect a secreted protein).
Could it be that the enzymes are modified post-translationally before or during transport (testable with MS)? In addition, intra- and extracellular environments are different, for example, cytosol is reducing while the external environment may be oxidizing (at least for aerobic species). This may affect the equilibrium between -SH and -S-S-, a hypothesis that could be tested with DTT,
Dr. Liger, it was from the same samples so definitely encoded by the same gene. But you are right, the extraction protocol is very harsh for intracellular enzymes while for extra-cellular it was coming out naturally.
Enzymes (proteins) are the cellular macromolecules that made the very fast regulatory responses to environmental (micro environmental as well) changes in order to preserve life. This can be done with the protein already purified therefore without any change in quantity or quality of DNA readings (gene expression). Proteins capable of these regulatory responses may present allosteric changes in conformation that in very resumed form, can be explained by the existence of R (relaxed = active conformation) and T (tense = inactive less active conformation) of the same protein (in real terms there must be much more conformations than these two). In order to compare enzyme activities usually, a single reaction mixture is used for the two measurements. This can be optimum condition for the extracellular (favoring its R form) and not quite for the enzyme harvested from the intracellular and /or the intracellular may have a larger portion in its T conformation that the one harvested from the extracellular. Transitions R – T may affect several aspects of enzyme activity: Vmax, Km, sensitivity to modifiers of activity etc…Only very time consuming and detailed study of optimal conditions on both enzymes could provide clear answer to your very interesting question. Different extraction procedures as pointed out by others, protection of S-S bridges as also pointed out, may be part of this time consuming effort required in order to have a good answer.
Thank you very much Dr. Roselino for focusing some light on the probable reasons. I appreciate your thinking and definitely further study is needed on your directed lines to get clear answer.
Rightly said by AKM if one is using same enzyme unit then, I also don't think they will show any differences in hydrolyzation.
But as suggested by Dominique Liger if the the secreted and cellular forms of enzymes are encoded by different genes that may account for different catalytic properties.
Further there are different genes for same enzyme in the same organisms/sample. We have isolated three gene for enzyme endoglucanase from single bacterium Paenibacillus sp. IHB B 3084.
http://www.sciencedirect.com/science/article/pii/S0141813015005310
http://www.sciencedirect.com/science/article/pii/S1381117715300163
Other factors like secretion and purification may also affect the catalytic properties.
A bacterial protein that is destined for secretion contains an N-terminal secretion signal sequence, which is removed subsequent to secretion by a signal peptidase. Therefore, the protein while it is still inside the cell prior to secretion differs in sequence from the same protein once it has been secreted. The presence of this signal sequence inside the cell may have a deleterious affect on the activity of the protein.
The intracellular environment is reducing, which means that cytoplasmic proteins rarely have disulfide bonds. Extracellular proteins are often in an oxidizing environment, and extracellular proteins frequently have disulfide bonds. A protein made in the cytoplasm but destined for secretion does not have its native disulfide bonds yet. If the protein is isolated at this point, especially if it is isolated in a buffer containing a reducing agent, it is not in its native disulfide-bonded state. This may also have a deleterious effect on the activity of the protein if the proper disulfide bonds do not form.
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