Human serum albumin

• Maintains oncotic pressure
• Transports thyroid hormones
• Transports other hormones, in particular, ones that are fat-soluble
• Transports fatty acids ("free" fatty acids) to the liver and to myocytes for utilization of energy
• Transports unconjugated bilirubin
• Transports many drugs; serum albumin levels can affect the half-life of drugs
• Competitively binds calcium ions (Ca²⁺)
• Serum albumin, as a negative acute-phase protein, is down-regulated in inflammatory states. As such, it is not a valid marker of nutritional status; rather, it is a marker of an inflammatory state
• Prevents photodegradation of folic acid
• Prevent pathogenic effects of Clostridium difficile toxins[2]

Serum albumin is commonly measured by recording the change in absorbance upon binding to a dye such as bromocresol green or bromocresol purple.[3]

Serum albumin concentration is typically 35–50 g/L (3.5–5.0 g/dL).[1]

It has been known for a long time that human blood proteins like hemoglobin[9] and serum albumin[10][11] may undergo a slow non-enzymatic glycation, mainly by formation of a Schiff base between ε-amino groups of lysine (and sometimes arginine) residues and glucose molecules in blood (Maillard reaction). This reaction can be inhibited in the presence of antioxidant agents.[12] Although this reaction may happen normally,[10] elevated glycoalbumin is observed in diabetes mellitus.[11]

Glycation has the potential to alter the biological structure and function of the serum albumin protein.[13][14][15][16]

Moreover, the glycation can result in the formation of Advanced Glycation End-Products (AGE), which result in abnormal biological effects. Accumulation of AGEs leads to tissue damage via alteration of the structures and functions of tissue proteins, stimulation of cellular responses, through receptors specific for AGE-proteins, and generation of reactive oxygen intermediates. AGEs also react with DNA, thus causing mutations and DNA transposition. Thermal processing of proteins and carbohydrates brings major changes in allergenicity. AGEs are antigenic and represent many of the important neoantigens found in cooked or stored foods.[17] They also interfere with the normal product of nitric oxide in cells.[18]

Although there are several lysine and arginine residues in the serum albumin structure, very few of them can take part in the glycation reaction.[11][19]

The albumin is the predominant protein in most body fluids, its Cys34 represents the largest fraction of free thiols within body. The albumin Cys34 thiol exists in both reduced and oxidized forms.[20] In plasma of healthy young adults, 70–80% of total HSA contains the free sulfhydryl group of Cys34 in a reduced form or mercaptoalbumin (HSA-SH).[21] However, in pathological states characterized by oxidative stress and during the aging process, the oxidized form, or non-mercaptoalbumin (HNA), could predominate.[22] The albumin thiol reacts with radical hydroxyl (.OH), hydrogen peroxide (H₂O₂) and the reactive nitrogen species as peroxynitrite (ONOO.), and have been shown to oxidize Cys34 to sulfenic acid derivate (HSA-SOH), it can be recycled to mercapto-albumin; however at high concentrations of reactive species leads to the irreversible oxidation to sulfinic (HSA-SO2H) or sulfonic acid (HSA-SO3H) affecting its structure.[23] Presence of reactive oxygen species (ROS), can induce irreversible structural damage and alter protein activities.

In the healthy kidney, albumin's size and negative electric charge exclude it from excretion in the glomerulus. This is not always the case, as in some diseases including diabetic nephropathy, which can sometimes be a complication of uncontrolled or of longer term diabetes in which proteins can cross the glomerulus. The lost albumin can be detected by a simple urine test.[24] Depending on the amount of albumin lost, a patient may have normal renal function, microalbuminuria, or albuminuria.

The approximate sequence of human serum albumin is:[25]

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

Of the 609 amino acids in this sequence, encoded by the ALB gene and translated to form the precursor protein, only 585 amino acids are observed in the final product present in the blood; the first 24 amino acids (here italicized), including the signal peptide (1–18) and propeptide (19–22, or 19–24) portions, are cleaved after translation.

Human serum albumin has been shown to interact with FCGRT.[26]

• Bovine serum albumin
• Serum albumin

• Human Albumin structure in the Protein data bank
• Human Albumin information in the Swis-Prot/TrEMBL database
• Human Serum Albumin on the Human Protein Reference Database
• Albumin binding prediction
• Albumin at Lab Tests Online
• Albumin: analyte monograph from the Association for Clinical Biochemistry and Laboratory Medicine