Path: utzoo!utgpu!watmath!iuvax!silver!chiaravi
From: chiaravi@silver.bacs.indiana.edu (Lucius Chiaraviglio)
Newsgroups: sci.bio
Subject: Re: Hybrid vigor
Summary: a few biochemical points to make
Keywords: ATP pool, "fast" and "slow" variants of an enzyme
Message-ID: <24513@iuvax.cs.indiana.edu>
Date: 11 Aug 89 03:32:38 GMT
References: <4869@drivax.UUCP> <3411@internal.Apple.COM> <5983@lynx.UUCP> <3452@internal.Apple.COM> <10659@boulder.Colorado.EDU>
Reply-To: chiaravi@silver.bacs.indiana.edu (Lucius Chiaraviglio)
Organization: Department of Biology at Indiana University, Bloomington
Lines: 40

In article <10659@boulder.Colorado.EDU> pell@boulder.Colorado.EDU (Anthony
Pelletier) writes:
>[. . .]
>If there were two common variants of Myosin Light-chain Kinase, one with a
>high Vmax and high Km(ATP), the other with the oposite profile, people with the
>former could contract the muscle with greater velocity, exerting
>greater thrust, but would fall below optimal ATP concentrations very rapidly
>during prolonged use; while people with the latter form would not be able to
>exert nearly the thrust, but could keep going longer.

	Actually, this won't do what you want.  The problem is that a cell
(especially a muscle cell running at full output) turns over its ATP supply in
seconds.  ATP is used as the common energy currency of the cell, but cells
don't hoard that much cash.  Instead, cells generate ATP as fast as they need
it, with the supply being tightly demand-controlled.  Running out of ATP does
not make a muscle cell tired, but rather causes it to go into rigor (as in
rigor mortis), because all the myosin heads stick to actin filaments and won't
let go.  Muscle cells normally prevent this from happening by means of a
safety mechanism that won't let them attempt to contract when they can't make
enough ATP to drive the contraction (I'm not sure of the details of this

>[. . .]
>So, what if, as for hemoglobin, one isoform exists at higher frequency
>in the black population than in the white?  So What?
>Is this notion really so disturbing?  Why should we treat it differently
>than, say, the difference in isoforms of Aldehyde Dehydrogenase between
>Whites and Asians? (Many Asians have a slow form that leads them to be
>sensitive to drinking alcohol)

	One should be careful with talking about "fast" and "slow" isoforms of
enzymes; while in this case it is fairly obvious that you are talking about
the rate at which the enzyme functions, "fast" and "slow" are often used to
refer to electrophoretic variants of an enzyme, whose speed of migration in an
SDS-polyacrylamide gel is entirely independant of their enzymatic turnover
rates!

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