Albumin

Albumin is a blood plasma protein that is produced in the liver and forms a large proportion of all plasma protein. Substances containing albumin, such as egg white, are called albuminoids.

The normal range of albumin concentrations in human blood is 3.5 to 5.0 g/dL, and albumin normally constitutes about 60% of plasma protein; all other proteins present in blood plasma are referred to collectively as globulin. Albumin is essential for maintaining the oncotic pressure needed for proper distribution of body fluids between intravascular compartments and body tissues. Albumin is negatively charged. The glomerular basement membrane is also negatively charged; this prevents the filtration of albumin in the urine. In nephrotic syndrome, this property is lost, and there is more albumin loss in the urine. Nephrotic syndrome patients are given albumin to replace the lost albumin.

Because smaller animals (for example rats) function at a lower blood pressure, they need less oncotic pressure to balance this, and thus need less albumin to maintain proper fluid distribution.

Albumin Amino Acid Sequence

The approximate sequence of human serum albumin is:

MKWVTFISLL FLFSSAYSRG VFRRDAHKSE VAHRFKDLGE ENFKALVLIA FAQYLQQCPF EDHVKLVNEV TEFAKTCVAD ESAENCDKSL HTLFGDKLCT VATLRETYGE MADCCAKQEP ERNECFLQHK DDNPNLPRLV RPEVDVMCTA FHDNEETFLK KYLYEIARRH PYFYAPELLF FAKRYKAAFT ECCQAADKAA CLLPKLDELR DEGKASSAKQ RLKCASLQKF GERAFKAWAV ARLSQRFPKA EFAEVSKLVT DLTKVHTECC HGDLLECADD RADLAKYICE NQDSISSKLK ECCEKPLLEK SHCIAEVEND EMPADLPSLA ADFVESKDVC KNYAEAKDVF LGMFLYEYAR RHPDYSVVLL LRLAKTYETT LEKCCAAADP HECYAKVFDE FKPLVEEPQN LIKQNCELFE QLGEYKFQNA LLVRYTKKVP QVSTPTLVEV SRNLGKVGSK CCKHPEAKRM PCAEDYLSVV LNQLCVLHEK TPVSDRVTKC CTESLVNRRP CFSALEVDET YVPKEFNAET FTFHADICTL SEKERQIKKQ TALVELVKHK PKATKEQLKA VMDDFAAFVE KCCKADDKET CFAEEGKKLV AASQAALGL

Where the italicized first 24 amino acids are signal and propeptide portions not observed in the transcribed and tranported protein but present in the gene. There are 609 amino acids in this sequence with only 585 amino acids in the final product observed in the blood.

Functions of Albumin

  • Maintains oncotic pressure
  • Transports thyroid hormones
  • Transports other hormones, particularly fat soluble ones
  • Transports fatty acids ("free" fatty acids)
  • Transports unconjugated bilirubin
  • Transports many drugs
  • Competitively binds calcium ions (Ca2+)
  • Buffers pH

Causes of Albumin Deficiency

  • Cirrhosis of the liver (most commonly)
  • Decreased production (as in starvation)
  • Excess excretion by the kidneys (as in nephrotic syndrome)
  • Excess loss in bowel (protein losing enteropathy)
  • Mutation causing analbuminemia (very rare)

Sources: DiaPharma, Wikipedia