Re: Hydrogenated Oils

[Guest guest]

>I really don't see how trans fats in the membrane can affect the cellular

>function, since they would have no contact with the inside or

>outside of the

>cell. The lipid portion of the cell is isolated in the center of

>the lipid

>bilayer and is non-polar,

so does not carry or contain charges,

>and faces only other

>lipids.

>

chris, i don't know what you mean by the the lipid portion being " isolated "

(OK - you must mean that the nonpolar ends face each other) but the lipid

bylayer has a number of proteins (called transmembrane proteins) passing

through it - so it's not isolated in that sense and the trans fats could

have contact with some of the transmembrane proteins that extend through the

bylayer. however, i have no idea if mere contact with proteins could have

any adverse effect - i'm just pointing out that they do likely have contact

with some transmembrane proteins.

further, transmembrane proteins do carry a charge if i'm not mistaken. and

these transmembrane proteins DO in fact interact with the hydrophobic tails

of the lipid bylayer (again according to MBC, p. 485).

and again - i'm not sure how trans fats incorporated into the lipid bylayer

would adversely affect the cell function other than that they might replace

more appropriate fatty acids that the membrane would select if they were

available. it's true that cholesterol molecules help to maintain membrane

fluidity, but i wonder if there aren't quite a few folks who might be

cholesterol deficient due to poor health. still, i don't know what the

effect would be if someone had a LOT of trans fatty acids incorporated into

cell membranes and deficient cholesterol molecules - other than the membrane

could become too flexible and lose some of its necesary rigidity. that would

be the case, i believe, with an excess of any PUFA - not just trans fatty

acids.

She

>said that charge is determined by the phophate head, not the lipid

>part, and

>that the ratio of saturated and unsaturated fatty acids in the membrane is

>strictly regulated, and that only small shifts can occur, which

>are compensated for

>by cholesterol inclusion/exclusion.

>

i've read that it's possible to affect membrane fluidity with PUFA

consumption. i wonder if that's true and if so, if it's mainly the case with

folks who are cholesterol deficient (as mentioned above), or have some other

abnormality interfering with membrane fluidity regulation.

>The enzymes that assemble the phospholipids are very specific and

>discriminate by specific fatty acid, and can't include other fatty

>acids " by accident. "

but what if the fatty acids they are specifically looking for aren't present

and in their absence, the enzymes select " replacements " ? that's analogous to

what rex harrill of the brix talk list was saying about plants - that, in

the abscense of appropriate minerals, they take up lead and other

" replacements " . is that a universal " rule " in biological systems, or am i

just engaging in wild extrapolation?

Suze Fisher

Lapdog Design, Inc.

Web Design & Development

http://members.bellatlantic.net/~vze3shjg

Weston A. Price Foundation Chapter Leader, Mid Coast Maine

http://www.westonaprice.org

----------------------------

" The diet-heart idea (the idea that saturated fats and cholesterol cause

heart disease) is the greatest scientific deception of our times. " --

Mann, MD, former Professor of Medicine and Biochemistry at Vanderbilt

University, Tennessee; heart disease researcher.

The International Network of Cholesterol Skeptics

<http://www.thincs.org>

----------------------------

[Guest guest]

In a message dated 1/29/04 12:19:47 AM Eastern Standard Time,

s.fisher22@... writes:

> however, i have no idea if mere contact with proteins could have

> any adverse effect - i'm just pointing out that they do likely have contact

> with some transmembrane proteins.

I can't see how that could possibly affect anything. The fatty acids are

non-polar, so they couldn't distort the shape of the protein (if they were polar

and charged, you could *conceivably* distort the shape of the protein

electrostatically, though the proteins move in the bilayer, so that's very, very

unlikely).

> further, transmembrane proteins do carry a charge if i'm not mistaken. and

> these transmembrane proteins DO in fact interact with the hydrophobic tails

> of the lipid bylayer (again according to MBC, p. 485).

Umm... you must have an old edition of the book. Page 485 is " The Size and

Subunit Composition of a Protein can be Determined by SDS Polyacrylamide-Gel

Electrophoresis. " Could you perhaps give me the chapter and heading instead of

the page number?

On 594 in my book it says:

" Like their lipid neighbors, these transmembrane proteins are amphipathic,

having regions that are hydrophobic and regions that are hydrophilic. Their

hydrophobic regions pass through the membrane and interact with the hydrophobic

tails of the lipid molecules in the interior of the bilaye, where they are

sequestered away from water. " (Membrane Proteins Can Be Associated With the

Lipid

Bilayer in Various Ways, Chapter 10: Membrane Structure)

But the fact that the non-polar regions of each are interacting means there

can't be a charged involved, because non-polar molecules do not carry partial

charges. (Actually, they do carry the transient flickering alternation of

dipole moments called van der Waals interactions, but that's overcomplicating

the

issue.) Also, the proteins and lipids both tend to do a *lot* of movement, so

it would seem that if a given fatty acid was unfavorable to bind with (for

whatever reason I can't grasp), it would just bump along until a favorable one

found its way to the protein.

> and again - i'm not sure how trans fats incorporated into the lipid bylayer

> would adversely affect the cell function other than that they might replace

> more appropriate fatty acids that the membrane would select if they were

> available.

That could only happen if they were similar enough to fool a highly specific

enzyme into thinking they are the corresponding saturated fats. In that case,

it would appear that they'd behave chemically similar to the saturated fats

in the membrane, if they behave as such in the enzyme.

it's true that cholesterol molecules help to maintain membrane

> fluidity, but i wonder if there aren't quite a few folks who might be

> cholesterol deficient due to poor health.

Cholesterol maintains rigidity at body temperature, not fluidity, so it would

only be needed to counter the effects of cis-unsaturated fats. I don't even

know why I brought it up, since I'd expect trans-unsaturated fats and

saturated fats to have the same effect on membrane fluidity.

still, i don't know what the

> effect would be if someone had a LOT of trans fatty acids incorporated into

> cell membranes and deficient cholesterol molecules - other than the membrane

> could become too flexible and lose some of its necesary rigidity. that would

> be the case, i believe, with an excess of any PUFA - not just trans fatty

> acids.

It would only be the case with an excess of cis-PUFA, not trans-PUFA, because

trans fats behave like saturated fats in terms of aggregation. They might

behave otherwise in terms of physiology, but their tendency to increase fluidity

or decrease it is the same as their tendency to be hard or fluid at room

temperature in a Crisco can. They're straight; thus, they increase rigidity.

It's doubtful that the cell membranes would just automatically include more

PUFA in the membranes if there's more in the diet. This might happen to a

certain degree, but after a certain point, the cell is just going to fall apart.

You can't just keep adding cholesterol, because you'll destroy the integrity

of the membrane by separating the fatty acids from each other. The body can

saturate most unsaturated fatty acids, and can manufacture saturated fats from

carbohydrates, so it would seem that it should be relatively equipped

regardless of the diet.

> i've read that it's possible to affect membrane fluidity with PUFA

> consumption. i wonder if that's true and if so, if it's mainly the case with

> folks who are cholesterol deficient (as mentioned above), or have some other

> abnormality interfering with membrane fluidity regulation.

I don't know; good question.

> >The enzymes that assemble the phospholipids are very specific and

> >discriminate by specific fatty acid, and can't include other fatty

> >acids " by accident. "

>

> but what if the fatty acids they are specifically looking for aren't present

> and in their absence, the enzymes select " replacements " ?

If the fatty acid doesn't fit the enzyme, it doesn't fit. An enzyme can't

just take whatever it wants, it's very specific.

that's analogous to

> what rex harrill of the brix talk list was saying about plants - that, in

> the abscense of appropriate minerals, they take up lead and other

> " replacements " . is that a universal " rule " in biological systems, or am i

> just engaging in wild extrapolation?

No, it isn't really analogous at all. You can't compare the function of an

ionic element to the function of an enormous macromolecule. Metal ions can be

very similar to each other when they have the same charge, differing only in

weight and radius, so they can fulfill many of the same functions (and also

cause problems). But large macromolecules such as proteins have incredibly

complex binding sites with astounding specificity. Molecules need to be able to

fit perfectly into the binding site to maximize the noncovalent bonds they can

form in order to be held in place, and you can't just trade one for another.

If you can, for example, trade an 18-carbon trans fat for an 18-carbon

saturated fat, that means that they behave similarly in geometry and charge

enough to

fool the enzyme, they can probably interact with any other protein just as

effectively. Since the binding site of an enzyme is far more specific and

intricate than the interaction with the side groups of transmembrane proteins,

it

seems unlikely that a trans fat could do the former just fine and fail at the

latter.

My teacher is going to try to find anything she can on trans fats

incorporated into the cell membranes in the literature for me.

Chris