Why is beta lactamase an inducible enzyme?

[doctor_p]

It's been written in my Microbiology textbook, that
"Pencillinase (or Beta lactamase) is an inducible enzyme."
Now, what is the use of it being an inducible enzyme?
Taking the example of lac-operon (which is an "inducible" operon), it works only if lactose is present in the medium and it actually "enters" the cells. Its "incoming" acts as a stimulus.

If we apply the same logic, it means that the penicillinase enzyme production can be induced if Penicillin actually enters the cells.
Now, if penicillin has entered the cell, it means that the cell has died. And if the whole cell itself as died, there would be nothing left for it to induce!

(I am an undergraduate - first year, so please answer accordingly.)

Thanks in advance.

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[Manual Disimpaction]

youre a freshman in undergrad but felt a medical student status was applicable to you?

 

[doctor_p]

youre a freshman in undergrad but felt a medical student status was applicable to you?

I'm in a medical college. What else should I call myself?
I'm not from the US. I don't know whom you call an undergraduate there, but here, a medical student is the one whose name's been enrolled in a medical college.

 

[Manual Disimpaction]

Roger that my mistake

 

[aim-agm]

Now, if penicillin has entered the cell, it means that the cell has died. And if the whole cell itself as died, there would be nothing left for it to induce!

This is probably where your reasoning went wrong, for two reasons:
1. Penicillin acts on cells that are growing/dividing. If a cell isn't, then it has a window to induce beta-lactamase before starting to grow and divide.
2. The more important (and broad) reason is that penicillin will be lethal to the cell once it has bound and inhibited enough transpeptidases to cause the cell wall to fail to sufficiently cross-link. That means that you have to get a certain amount of penicillin molecules into the cell and that takes time. If beta-lactamase is induced early it can keep intracellular penicillin concentrations too low to be deadly.

 

[petrosgp]

This is probably where your reasoning went wrong, for two reasons:
1. Penicillin acts on cells that are growing/dividing. If a cell isn't, then it has a window to induce beta-lactamase before starting to grow and divide.
2. The more important (and broad) reason is that penicillin will be lethal to the cell once it has bound and inhibited enough transpeptidases to cause the cell wall to fail to sufficiently cross-link. That means that you have to get a certain amount of penicillin molecules into the cell and that takes time. If beta-lactamase is induced early it can keep intracellular penicillin concentrations too low to be deadly.

I thought Penicillin acts on cells even when they are not dividing, since bacteria are constantly breaking down and rebuilding their cell wall?

 

[deleted763299]

It's been a while since I've studied micro, but here's my answer...

if penicillin has entered the cell, it means that the cell has died

This is untrue. Antibiotics such as penicillin do not kill bacteria instantly upon entry. Furthermore, in order to kill bacteria an antibiotic must reach a sufficiently high concentration, called its minimum inhibitory concentration (MIC). After administration of an antibiotic, it does not immediately achieve its MIC. I'm not sure if you've had any pharmacology yet, but (as with all drugs) the antibiotic must be absorbed, distributed, and diffuse into its effect site (in the case of an antibiotic, the infected tissues). That was a long-winded way to say that bacteria have some time between the antibiotic's arrival, and their possible death.

Now, what is the use of it being an inducible enzyme?

To constantly produce beta-lactamase, regardless of whether or not penicillin (or some other beta-lactam) is present would be an evolutionary disadvantage to a bacterium. Generally speaking, bacteria do not have large quantities of excess resources at their disposal. Protein synthesis is a significant energy expenditure, and requires amino acids (another important cellular resource). To constantly produce a protein that the bacterium is not constantly using would be a considerable handicap, and such a bacterium would be out-performed by more efficient organisms.

 

[WedgeDawg]

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