Substrates and Conjugates
17/05/10 14:53
I could tell you guys to go look up these words in the glossary, but we don’t have the glossary online yet, so I’ll give you a little course in them.
Substrates are the substances that a protein, or an enzyme, acts upon. If you have a protein, like the CFTR and the MRP, that is supposed to transport a substance across a membrane, into the extracellular space, then it’s substrates are the substances that it transports. For instance, the CFTR transports glutathione, while the MRP transports glutathione attached to another compound, such as a chemotoxin. Both glutathione and glutathione attached to another compound are the substrates of the proteins CFTR and MRP, but the latter—glutathione attached to a chemotoxin—is both a substrate and a conjugate.
In the case of the CFTR protein, it’s substrates are all anions—negatively charged ions. In the case of MRP, it’s substrates are usually the same anions that are transported by the CFTR protein, but they are attached to another compound. Together, the anion and the other compound, are conjugates. Another term for these conjugates is “adducts.” For instance, when you have a glutathione adduct of a chemotoxin, you call it the glutathione adduct of whatever chemotoxin you are talking about. You can have the glutathione adduct of any compound that will accept the extra electron on glutathione. Once they form a bond, they are a conjugate, or an adduct.
The boy who had both CF and cancer; the one who started us all off on this venture, was taking chemotoxins. His cells began to express MRP proteins, because of these chemotoxins, and the glutathione in his cells formed conjugates with the chemotoxins and these conjugates were transported out of the cell by the MRP proteins.
The cool thing about this is that the MRP proteins also have, as substrates, the oxidized form of glutathione, called glutathione disulfide, or GSSG. And, in the place that the GSSG is transported, the extracellular space (the airways), there are chemicals that turn GSSG right back into it’s reduced form: GSH. So, when the boy who was taking chemotoxins to fight his cancer started making MRP proteins, and those proteins started transporting glutathione adducts of the chemotoxins, they also transported GSSG. And, once that GSSG got to the extracellular space, it was turned right back into GSH.
That’s the idea behind aerosolizing GSH into the airways. But, it’s not a good idea. Why? Because the amount of GSH in the airways is up and down, depending on other conditions. When you aerosolize it, you are giving GSH not just to the CF patient, but you are giving it to all of the pathogens that use it to conjugate antibiotics that are supposed to kill the pathogen. The pathogen uses it, too, especially if there is a lot of it out there. Normally, the amount of GSH in the airways would be regulated by pump proteins, like the CFTR and the MRP. But, that regulation is gone, if you aerosolize it directly into the airways.
Once you have those proteins in the membrane of the cell, you can pump out not just GSH and GSH conjugates, but all of the substances that are substrates of that protein; and they compete with each other. You won’t be just pumping out GSH conjugates, but also sulfate conjugates, thiocyanate, bicarbonate, glucuronic ion and chloride. The trick is to get those proteins into the membrane of the cell.
In CF, the CFTR is mutated, and in most cases, never makes it out of the organelle that it’s made in—the endoplasmic reticulum—because it’s folded improperly and the chemical messengers that take it through the endoplasmic reticulum, to get it matured, sense that it is not folded properly, and hold it back there, to be chopped up and destroyed there. It never “traffics” to the membrane, where it’s supposed to sit and do it’s job. But this is not the case with the MRP proteins. They make it to the membrane.
And, once there, they use what would normally be CFTR substrates to combine with other substances, to form conjugates, and these conjugates are pumped out via the MRP. The great thing about this is that those CFTR substrates are still pumped out to the airways, in a different (conjugate) form, but they are still getting to where they belong.
Substrates are the substances that a protein, or an enzyme, acts upon. If you have a protein, like the CFTR and the MRP, that is supposed to transport a substance across a membrane, into the extracellular space, then it’s substrates are the substances that it transports. For instance, the CFTR transports glutathione, while the MRP transports glutathione attached to another compound, such as a chemotoxin. Both glutathione and glutathione attached to another compound are the substrates of the proteins CFTR and MRP, but the latter—glutathione attached to a chemotoxin—is both a substrate and a conjugate.
In the case of the CFTR protein, it’s substrates are all anions—negatively charged ions. In the case of MRP, it’s substrates are usually the same anions that are transported by the CFTR protein, but they are attached to another compound. Together, the anion and the other compound, are conjugates. Another term for these conjugates is “adducts.” For instance, when you have a glutathione adduct of a chemotoxin, you call it the glutathione adduct of whatever chemotoxin you are talking about. You can have the glutathione adduct of any compound that will accept the extra electron on glutathione. Once they form a bond, they are a conjugate, or an adduct.
The boy who had both CF and cancer; the one who started us all off on this venture, was taking chemotoxins. His cells began to express MRP proteins, because of these chemotoxins, and the glutathione in his cells formed conjugates with the chemotoxins and these conjugates were transported out of the cell by the MRP proteins.
The cool thing about this is that the MRP proteins also have, as substrates, the oxidized form of glutathione, called glutathione disulfide, or GSSG. And, in the place that the GSSG is transported, the extracellular space (the airways), there are chemicals that turn GSSG right back into it’s reduced form: GSH. So, when the boy who was taking chemotoxins to fight his cancer started making MRP proteins, and those proteins started transporting glutathione adducts of the chemotoxins, they also transported GSSG. And, once that GSSG got to the extracellular space, it was turned right back into GSH.
That’s the idea behind aerosolizing GSH into the airways. But, it’s not a good idea. Why? Because the amount of GSH in the airways is up and down, depending on other conditions. When you aerosolize it, you are giving GSH not just to the CF patient, but you are giving it to all of the pathogens that use it to conjugate antibiotics that are supposed to kill the pathogen. The pathogen uses it, too, especially if there is a lot of it out there. Normally, the amount of GSH in the airways would be regulated by pump proteins, like the CFTR and the MRP. But, that regulation is gone, if you aerosolize it directly into the airways.
Once you have those proteins in the membrane of the cell, you can pump out not just GSH and GSH conjugates, but all of the substances that are substrates of that protein; and they compete with each other. You won’t be just pumping out GSH conjugates, but also sulfate conjugates, thiocyanate, bicarbonate, glucuronic ion and chloride. The trick is to get those proteins into the membrane of the cell.
In CF, the CFTR is mutated, and in most cases, never makes it out of the organelle that it’s made in—the endoplasmic reticulum—because it’s folded improperly and the chemical messengers that take it through the endoplasmic reticulum, to get it matured, sense that it is not folded properly, and hold it back there, to be chopped up and destroyed there. It never “traffics” to the membrane, where it’s supposed to sit and do it’s job. But this is not the case with the MRP proteins. They make it to the membrane.
And, once there, they use what would normally be CFTR substrates to combine with other substances, to form conjugates, and these conjugates are pumped out via the MRP. The great thing about this is that those CFTR substrates are still pumped out to the airways, in a different (conjugate) form, but they are still getting to where they belong.