Re: Endothermy

[TomHopp@aol.com]

In a message dated 9/5/98 7:02:05 AM, chris.lavers@nottingham.ac.uk wrote:

<<There has been talk on the list of uncoupling proteins, their role in
generating heat and the molecular systematics thereof. Does anyone have any
references? Any help would be much appreciated.>>

Chris, the ENTREZ database of genome sequences lists over 400 references to
uncoupling proteins. You might start there, or in a biochemistry textbook, for
references that will lead you to enlightenment. I checked the database and
surprised myself with what was to be found there. Not only have three
different forms of the gene been found (so far) but sequences are known for
human, mouse and rat uncoupling proteins (the usual suspects) and other
species like rabbit, hamster, cow, sheep, as well. The field is clearly
exploding, and I think I know why. Several papers refer to the ability to
"burn fat." No wonder several patents are listed in the database. There's gold
in them thar genes.
   Along the way, some shockers have appeared.  There are already two reports
of PLANTS (potato and the weed, Arabidopsis) having these proteins, for heat
generating purposes, so my exchange with Tom Holtz on skunk cabbage heat
generation seems prescient (or perhaps post-scient since the facts had already
been published). Therefore, when we discuss the possibility of endothermy
ARRISING, we need to consider that there appears to be a complex, and VERY
ANCIENT web of metabolic mechanisms which can be used to generate heat. I am
more than ever convinced that ectothermy and endothermy, rather than being
primitive and advanced, respectively, are just metabolic options, used to meet
the needs of an organism's particular lifestyle.
    The following is an interesting out-take from my web search:

<Dr. K.B.Freeman Professor, Department of Biochemistry B.A., Ph.D. (Toronto)
UNCOUPLING PROTEIN: STRUCTURE/ FUNCTION RELATIONSHIPS AND MITOCHONDRIAL
IMPORT. Uncoupling protein of mammalian brown adipose tissue mitochondria has
the unique function of regulated uncoupling of oxidative phosphorylation in
the tissue resulting in heat production. This serves a protective function for
small mammals and the newborn including humans during cold stress. The tissue
might also be important in preventing obesity by burning off excess calories.
Uncoupling protein uncouples by transporting protons or, since it transports
anions, by transporting the fatty acid anion.>

And here's the phytological show-stopper:

<AtPUMP: an Arabidopsis gene encoding a plant uncoupling mitochondrial 
protein. Maia IG, Benedetti CE, Leite A, Turcinelli SR, Vercesi AE, Arruda P.
FEBS Lett 1998 Jun 16;429(3):403-406. 

A cDNA clone (AtPUMP) encoding a plant uncoupling mitochondrial protein 
was isolated from Arabidopsis thaliana. The cDNA contains an open reading
frame of 921 nucleotides encoding 306 amino acids (predicted molecular weight
32,708). The predicted polypeptide is 81% identical and 89% similar to the
potato UCP-like protein, and includes an energy transfer protein motif common
to mitochondrial transporters. The AtPUMP gene exists as a single copy in the
Arabidopsis genome. The corresponding transcript was expressed in all tissues
and was strongly induced by cold treatment. We suggest that the putative
AtPUMP protein may play a role in heat-requiring physiological events in
Arabidopsis.>

Curiouser and curiouser.
    Tom Hopp