From Wikipedia, the free encyclopedia
Sodium-dependent glucose cotransporters are a
family of glucose transporter found in the
intestinal mucosa of the small intestine (SGLT1) and the proximal tubule
of the nephron (SGLT2 and
SGLT1). They contribute to renal glucose
SGLT1 and SGLT2 are members of the SLC5A gene family.
in proximal tubule
|Contribution to glucose
||predominately in the
S1 and S2 segments
Including SGLT1 and SGLT2, there are total seven members in the
human protein family SLC5A, several of which may also be
These proteins use the energy from a downhill sodium gradient to
transport glucose across the
apical membrane against an
uphill glucose gradient. Therefore, these co-transporters are an
example of secondary active transport.
(The GLUT uniporters then transport the glucose
across the basolateral membrane, into the peritubular capillaries.) Both
SGLT1 and SGLT2 are known as symporters since both sodium and glucose are
transported in the same direction across the membrane.
In August 1960, in Prague, Robert K. Crane presented for the first
time his discovery of the sodium-glucose cotransport as the mechanism for
intestinal glucose absorption.
discovery of cotransport was the first ever proposal of
flux coupling in biology.
the sodium-glucose cotransporter SGLT1
Co-transport proteins of mammalian cell membranes had eluded
efforts of purification with classical biochemical methods until
the late 1980's. These proteins had proven difficult to isolate
since they contain hydrophilic and hydrophobic sequences and exist
in membranes only in very low abundance (<0.2% of membrane
proteins). The rabbit form of SGLT1 was the first mammalian
co-transport protein ever to be cloned and sequenced and this
scientific break-through was reported in 1987. To circumvent the
difficulties with traditional isolation methods, Swiss-born
biochemist Matthias Hediger and his collaborators at UCLA used a novel
technique of expression cloning. They
size-fractionated large amounts of rabbit intestinal mRNA with a
preparative gel electrophoresis device developed by Hediger. These
size fractions were then sequentially injected into Xenopus oocytes to ultimately
find the RNA species that induced the expression of sodium-glucose
- ^ Wright EM, Hirayama BA, Loo DF (January
2007). "Active sugar transport in health and disease". J.
Intern. Med. 261 (1): 32–43. doi:10.1111/j.1365-2796.2006.01746.x. PMID 17222166.
- ^ Wright EM (January 2001). "Renal
Na(+)-glucose cotransporters". Am. J. Physiol. Renal
Physiol. 280 (1): F10–8. PMID 11133510.
Ensembl release 48: Homo
sapiens Ensembl protein family ENSF00000000509
Miller D, Bihler I (1961). "The
restrictions on possible mechanisms of intestinal transport of
sugars". in Kleinzeller A. Kotyk A. Membrane Transport and
Metabolism. Proceedings of a Symposium held in Prague, August
22–27, 1960. Czech Academy of
Sciences & Academic Press. pp. 439-449.
- ^ Wright EM, Turk E (February 2004). "The
sodium/glucose cotransport family SLC5". Pflugers Arch.
447 (5): 510–8. doi:10.1007/s00424-003-1063-6. PMID 12748858. "Crane in 1961
was the first to formulate the cotransport concept to explain
active transport . Specifically, he proposed that the
accumulation of glucose in the intestinal epithelium across the
brush border membrane was coupled to downhill Na+ transport cross
the brush border. This hypothesis was rapidly tested, refined and
extended [to] encompass the active transport of a diverse range of
molecules and ions into virtually every cell type.".
- ^ Boyd CA (March 2008). "Facts, fantasies
and fun in epithelial physiology". Exp. Physiol.
93 (3): 303–14. doi:10.1113/expphysiol.2007.037523. PMID 18192340. "p. 304. “the
insight from this time that remains in all current text books is
the notion of Robert Crane published originally as an
appendix to a symposium paper published in 1960 (Crane et al.
1960). The key point here was 'flux coupling', the cotransport of sodium
and glucose in the apical membrane of the small intestinal
epithelial cell. Half a century later this idea has turned into one
of the most studied of all transporter proteins (SGLT1), the
- ^ Hediger MA, Coady MJ, Ikeda TS, Wright EM
(1987). "Expression cloning and cDNA sequencing of the Na+/glucose
co-transporter". Nature 330 (6146):