lactase - lactose connection

Ouabache

Can someone help me find out how much lactase will breakdown a gram of lactose? I asked at our public library, with no success.
(Please cite reference: e.g text, Biochem course, personal experiment data...)

I am trying to make a calculation and created thread lactase query on the chemistry topic, but have not received any replies. Perhaps the readership there has expertise in other areas, outside of biochemistry.

Thanks for your thoughts and comments..

misskitty

I'd like to know the answer to your question as well. It might help me manage better. Just out of curiousity, how are you making your calculations?

~Kitty

Ouabache

So as not to bias the replies to my query, I'll send you my present calculations, by private message.

misskitty

Makes sense. Still, why the interest in how much it will take to break down one gram of lactose?

~Kitty

quetzalcoatl9

do a pubmed search for kinetic studies of lactase, i'm sure you'll find what you're looking for.

i think it's a safe bet that the lactase will break down all of the lactose, it is just a question of how long it will take and the dependence upon concentrations of lactase and lactose.

iansmith

Kinetics will also depend on the temperature.

Ouabache

Knowing how much lactase is needed to break down a specific weight of lactose, provides information to treat liquid dairy with any source of the enzyme, not just Lactaid caplets. As you may know, if you predigest the lactose in liquid diary, those with lactose intolerance can eat them without any concern.

Ouabache

Thanks for suggestion. I'm not really concerned how long the reaction will take, more that I am using enough enzyme. I also realize enzymes have a shelf life. It would be nice to know at what rate this potency diminishes? I imagine environmental factors (temp, humidity, time...) are variables of that equation.

Besides its probable affect on shelf life, iansmith points out that temperature is a variable of reaction kinetics.

misskitty

Sometimes the lactose doesn't always work. It has happened to me even when I have taken enough. Sometimes the lactase enzyme doesn't always break down everything even if you haven't pushed yourself over LI limit.

Typically with the over the counter Lactaid it says if you are eating foods containing Lactose for more than 30 minutes you'll need to take more lactaid for it to continue working. From personal experience I can say that Lactaid works for between 30-45 minutes. Never longer than 45 minutes. Usually it works for 35 minutes, less if the food you are eating has more lactose in it.

~Kitty

quetzalcoatl9

theoretically, one molecule of enzyme will catalyze the breakdown of the entire gram of lactose (if given enough time). see what i mean?

open a book to the topic of enzyme kinetics. look at a lineweaver-burk plot for instance. i would imagine that lactase has been well studied already.

as is pressure...but we really don't care about that. if we consider constant temp and pressure then what is important are the concentrations.

misskitty

Well yes considering that pressure and temperature has an affect on the concentrations of the lactase enzyme.

One molecule would breakdown a gram of lactose if it was potent enough and had a long enough period of time and if the conditions for that to happen were good.

~Kitty

Ouabache

Yes I am thinking lactase would be well studied too. You are shaking a few cobwebs out of my head, mentioning Lineweaver-Burk plots. I just looked at a reference and recognize the general form from bygone biochemistry courses. Looking at them now, I realize I didn't fully appreciate the underlying principles of the variables. (But I could generate some great plots on exams )

Another idea I was reminded of, is that enzymes are catalysts. (also recall that from high school biology) They lower the activation energy needed to convert a substrate by binding with the substrate, changing its conformation to enable further breakdown to occur, without being changed in the process.

So how does the conversion of lactose proceed in a milk emulsion?
An NIH site describes, "Adding a few drops of the enzyme will convert the lactose in milk or cream, making it more digestible for people with lactose intolerance."
At least in bacteria (and reasonable assumption, we share this pathway); in the metabolism of lactose, other enzymes are synthesized and used in conversion, such as lactose permease which actively transports the sugar molecules into the cell; and beta galactosidase which cleaves lactose into galactose and glucose. These simple sugars can enter subsequent metabolic pathways to generate energy, etc..

So if these metabolic steps occur in vivo; I wonder what exactly does lactose convert to, in enzyme treated milk? Perhaps the lactase is just binding with all the lactose present, so the converted lactose is just "lactase-bound-lactose". Then we would surely need more than one molecule of lactase

quetzalcoatl9

no, they don't. while the volume of the solution could change (and yes that could technically change the concentration), the mols of enzyme will be the same.

for example, you could compress the solution and cool it and get exactly the same kinetics. what pressure and temperature affect are the kinetic motions of the molecules in solution (from a classical perspective).

temperature or pressure could possibly, argueably, increase or decrease the solubility of the protein or solute, thereby raising the 'virtual' concentration, but that should not be the case in such a study since the solubility should be as close to complete as possible through use of ionic strength buffers, detergents, etc.

quetzalcoatl9

galactose and glucose i believe.

Ouabache

How? Doesn't that require Beta galactosidase ?
I don't believe that enzyme is found in milk.

iansmith

There bacteria found in milk that have beta-galactosidase. However, these bacteria are in smaller number in pasteurized milk and grow very slowing at 4C.

quetzalcoatl9

lactase and galactosidase are the same enzyme - different names.