Human Albumin

Methods of Preparation:
Sigma-Aldrich produces human serum albumin using a cold alcohol fractionation process derived from the traditional Cohn^1,3 method as well heat shock methods.^2,4

Molecular Weight:
66,437 Da 8 (based on amino acid composition). Commercial preparations contain varying degrees of post-translational modifications and genetic variants with molecular weight components mainly in the range of 66,437 to 66,600 Da

Structure:⁵
Human albumin is a single peptide chain with one free sulfhydryl group on residue # 34 and 17 intrachain disulfide bonds.

Mass Spec Analysis of various commercial preparations indicates the presence of several post-translational modifications. Native human serum albumin is not a glycoprotein in the traditional sense. However, several genetic variants exist that may undergo enzymatic N-& O-glycosylation. Upon circulation in plasma, albumin often becomes glucosylated on ε amine groups of lysine and possibly arginine residues. This is the result of the non-enzymatic spontaneous Maillard Reaction between the carbonyl group of the open ring form of glucose, present in small amounts in plasma, forming a Schiff base with the exposed primary amines of circulating proteins such as albumin, insulin and hemoglobin. Sigma has also observed various degrees of glucosylation in recombinant preparations. Cysteinylation is also present in native and recombinant preparations.

Amino Acid Composition

Amino Acid	Asp	Asn	Thr	Ser	Glu	Gln	Pro	Gly	Ala	Cys	Val	Met	Ile	Leu	Tyr	Phe	His	Lys	Trp	Arg
Residues	39	15	30	22	60	23	25	12	63	35	39	6	8	61	18	30	16	58	1	23

Fatty Acid Composition of Human Albumin.
Circulating plasma albumin typically contains 0.5-1.5 moles of fatty acid bound to one mole of albumin. Upper ranges of 4-9 moles per mole have been reported.^9,10 Alternatively, Sigma offers fatty acid depleted native human albumins.

Saturated Fatty Acids		Native .HSA	rHSA expressed in Rice
Lauric	12:0	<1%	0.2%
	13:0	<1%
Myristic	14:0	1.50%	1.5%
Pentadecenoic	15:0	< 1%	0.1%
Palmitic	16:0	24.70%	12.5%
	17:0	<1%
Stearic	18:0	1.50%	0.5%
Arachidic	20:0	<1%	0.0%
Bohenic	22:0	Not Tested	0.0%
Lignoceric	24:0	Not Tested	0.0%
Monosaturated Fatty Acids
Myristoleic	14:1	<1%	0.0%
Palmitoleic	16:1w7	<3.1%	0.8%
Oleic	18:1w9	<33.1%	35.9%
	18:1w7	<1%	0.0%
	24:1	<1%	0.0%
Diunsaturated Fatty Acids
Linoleic	18:2w6	<20.0%	44.8%
Polyunsaturated Fatty Acids
α-Linolenic	18:3w3	<1%	3.6%
	18:3w6	<1%	0.0%
	20:1w9	<1%	0.0%
	20:1w9	<1%	0.0%
	20:2w6	<1%	0.0%
	20:3	1.40%	0.0%
Arachidonic	20:4	5.00%	0.0%
	20:5	<1%	0.0%
	22:1w9	<1%	0.0%
	22:4w6	<1%	0.0%
	22:5w6	<1%	0.0%
	22:5w3	<1%	0.0%
	22:6w3	<1%	0.0%

Physical Properties⁵

Sedimentation constant, S20,W X 1013	4.6 (monomer), 6.5 (dimer)
Diffusion constant, D20,W X 107	6.1
Partial specific volume, V20	0.733
Intrinsic viscosity, η	0.042
Frictional ratio, f/f0	1.28
Overall dimensions, Å	38 X 150
Isoelectric point (Γ/2 = 0.15)	4.7
Isoionic point (Γ/2 = 0)	5.2
Electrophoretic mobility, pH 8.6, G/2 = 0.15	-5.9
Refractive index increment (578 nm) X 10-3	1.89
Optical absorbance, A279 nm (1 gram/liter)	0.531
Mean residue rotation, [m']233	8590
Mean residue ellipticity	17 [q]209 nm; 16 [q]222 nm
Estimated α-helix, %	48
Estimated β-form, %	15

Applications and Other Properties⁷
Due to its high charge to mass ratio, albumin binds water, Ca²⁺, Na⁺, K⁺, fatty acids, bilirubin, hormones and many xenobiotic drugs. The main biological function of albumin is to regulate the colloidal osmotic pressure of blood. Human and bovine albumins contain 16% nitrogen and are often used as standards in protein calibration studies. Due to their free hydrophobic region, fatty acid free albumins are used to solubilize lipids in tissue culture, and are also used as blocking agents in Western blots or ELISA applications. Globulin free albumins are suitable for use in applications where no other proteins should be present (e.g., electrophoresis).

References

1. E.J. Cohn, J. Amer. Chem. Soc., 68, 459 (1946).
2. R.F. Chen, J. Biol. Chem., 242, 173 (1967).
3. E.J. Cohn, J. Amer. Chem. Soc., 69, 1753 (1947).
4. Globulins are precipitated in a heat step following addition of caprylate, then removed by filtration.
5. The Plasma Proteins, 2nd Ed., Vol. I, F. W. Putnam, Ed., pp. 133-181, Academic Press, New York (1975).
6. S.C. Gill and P.H. von Hippel, Anal. Biochem., 182, 319 (1989).
7. T. Scott and M. Eagleson, Concise Encyclopedia: Biochemistry, 2nd Ed., pp. 19-20, Walter de Gruyter, New York (1988).
8. Sigma calculation based on sequence given by B. Meloun, et. al., FEBS Letters, 58(1), 134 (1975).
9. The free fatty acids bound to human serum albumin. Saifer, A., Goldman, L., J. Lipid Res., 2, 268-270 (1961)
10. Fatty acid enhancement of human serum albuminbinding properties. J. Biol. Chem., 252, 4043-4048 (1977)