Question about enzymes

Hi all,

I'm taking an introductory biology course, and I've been told
that enzymes always have only one active site.

I'm not sure about this however, because it seems to me
that there must be some enzyme that has 2 or more,
after all it's just a lumpy 3-dimensional tangle of protein,
so why wouldn't there be more than 1 active site?
For every shape on an enzyme there must be
some chemical that fits in there, right?

Can anyone please explain why an enzyme is only
expected to have one active site?

Thanks!

On 16 Oct 2006 10:19:14 -0700, [Only registered users see links. ] wrote:


It is not easy for evolution to figure out a way of making a chain of
specific amino acids in a specified sequence produce a complex
three-dimensional object that actually does something. And then
evolution has to figure out how to make it do that thing very well,
indeed. It really is asking too much to have it do two things at the
same time!

Ordinarily, enzymes catalyze one specific reaction (or category of
reactions) using one specific precursor (or category of precursors).
This bind at one specific active site to make things happen. That
doesn't mean that the enzyme doesn't also have all sorts of other
binding sites where other things can bind and influence the reaction
that occurs at the "real" active site. In fact it is quite common for
binding of ligands at a second site, or the phosphorylation of an
amino acid at a second site, to have very large consequences on the
function of the enzyme. It is just that the enzyme really only
catalyzes one reaction.

Note: just because a ligand happens to "fit into" and even "bind" to
a second site doesn't necessarily mean that anything will happen as a
result. Hence it isn't really a site at all, just an accidental and
incidental binding.

Ah, but what I'm getting at is that the behavior of complex molecules
is technically independent of evolution, so although organisms may
make use of a given active site, there may be others that either
are used, or not.

Anyway I googled for "multiple active sites" and enzyme, and
quite a few references appeared to enzymes that have them,
but I will have to look over the webpages to see if it's just
semantics or really multiple active sites.

For example:
[Only registered users see links. ]

[Only registered users see links. ] wrote:

Why is the behaviour of complex molecules independent of evolution?

Chris

In article <1161019154.389534.46130@m73g2000cwd.googlegroups. com>,
<[Only registered users see links. ]> wrote:

Are you sure you understood the answer, or your insstructor understood the
question?

Check out leukotriene A4 hydrolase, among other counterexamples.

Ian

--
Ian York ([Only registered users see links. ]) <http://www.panix.com/~iayork/>
"-but as he was a York, I am rather inclined to suppose him a
very respectable Man." -Jane Austen, The History of England

[Only registered users see links. ] wrote:


Evolution is not a thinking mechanism that exerts
conscious control, but is a problem-solving mechanism.

Ian A. York wrote:


I think she just didn't want the students to get confused.


Fascinating.

Here's info for anyone who's curious:
[Only registered users see links. ]

<[Only registered users see links. ]> wrote in message
news:1161028256.974864.264800@e3g2000cwe.googlegro ups.com...

Yes but is the behaviour of complex molecules independent of evolution ? Is
it not that the structure and fucntion of complex biological molecules are
actual products of evolution or do you have some other explaination ?

N10: )

[Only registered users see links. ] wrote:

Can you think of any problems that are solved with enzymes?

Chris

N10 wrote:


I think that if by random mutation a new protein arises,
and it serves as an enzyme and one of its active sites
benefits the organism, then it may be that any additional
active sites and associated functions that it also has may be
unused or underused under normal circumstances.
Evolution doesn't say "one enzyme, one function".
If an enzyme hypothetically has 3 active sites and functions,
and offers has great benefits but the other two are
mildly problematic, then the gene that codes for the enzyme
will be passed on.