N-Homocysteinyl-Proteins - Homocysteine in Protein Structure/Function and Human Disease - page 62

Table 5.4 Levels of N-linked Hcy in different proteins (Compiled from [79, 297])
Specie Protein (Mw, kDa) N-Hcy/protein, mol/mol 1,000

Human Ferritin (443) 470 20

Hemoglobin (64) 14.1 4.1

Albumin (68) 3.6

γ -Globulin (150) 3.6

Fibrinogen (340) 1.0

LDL (500) 1.0

Transferrin (80) 0.8

Antitrypsin (51) 0.7

HDL (150) 0.4

Horse Ferritin (443) 515 75

Apoferritin (443) 480 70

Catalase (250) 9.0

Myoglobin (17.1) 1.44 0.04

Cytochrome c (11.8) 1.07 0.17

Aldolase (25.3) 2.1

Bovine Thyroglobulin (669) 25.3 2.0

α-Crystallin (36) 2.6 1.3

Histone (15) 0.33 0.05

Carbonic anhydrase (29) 0.2

Pig Esterase (60) 13.0 2.5

Elastase (26.4) 4.16 1.12

Acylase (45) 2.85 0.00

Chicken Ovalbumin (45) 3.82 1.80

Lysozyme (17) 0.06

5.2.1.1 Cellular Proteins

Commercially available purified proteins each contain N-linked Hcy, at levels as
high as 0.470 and 0.515 mol Hcy/mol protein for human and equine ferritins,
respectively, to as low as 0.00006 mol Hcy/mol protein for chicken lysozyme
(Table 5.4 ). Similar levels of N-linked Hcy are found in iron-loaded ferritin and
iron-free apoferritin (Table 5.4 ), indicating that the presence of iron does not
interfere with the assay used. Most proteins contain intermediate levels of N-linked
Hcy, from about 0.001 mol Hcy/mol protein for cytochrome c and myoglobin to
0.01-0.025 mol Hcy/mol protein for catalase, esterase, and thyroglobulin.

5.2.1.2 Blood Proteins

Examination of purified human blood proteins demonstrates that normal human
hemoglobin, serum albumin, and -globulins contain 0.0036-0.0060 mol N-Hcy/

mol protein, while fibrinogen, LDL, HDL, transferrin, and antitrypsin contain lower
levels, 0.0004-0.0010 mol N-Hcy/mol protein [79]. Recalculation of these values
(by taking into account normal levels of individual blood proteins) shows that the

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