N-Homocysteinyl-Proteins - Homocysteine in Protein Structure/Function and Human Disease - page 65

Table 5.8 N-linked Hcy and S-linked Hcy levels in human hair keratin [308]
Gender
(n)

N-Hcy, pmol/mg
hair

S-Hcy, pmol/mg
hair

N-Hcy/(N-Hcy + S-
Hcy)

SDS-soluble N-Hcy
fraction

Female
(11)

95 39 126 41 0.36 0.10 0.38 0.08

Male (7) 82 41 181 64 0.31 0.11 0.49 0.09

exhibit connective tissue abnormalities similar to those observed in CBS-deficient
human patients [46]. Collagen prepared from the skin of these mice using the acetic
acid extraction method shows protein bands characteristic of type I collagen on SDS-
PAGE gels. Analysis of N-linked Hcy content in these collagen preparations shows that
Tg-I278T Cbs / mice have 18-fold higher skin N-Hcy-collagen levels than Tg-I278T
Cbs +/+ littermates (89.9 2.4 pmol/mg skin) [306]. Similar elevation

in N-linked Hcy in the Cbs-deficient mice is observed in bone collagen. These findings
demonstrate that collagen is a target for N-homocysteinylation in vivo in mice [306].

25.1 vs. 5.0

5.2.1.4 Milk Protein

The N-linked protein Hcy has also been discovered in other biological fluids. For
example, commercial cow milk contains 1.09 0.01 μM protein N-linked Hcy and
3.45 0.25 μ M tHcy, whereas cow whey contains 1.51 0.34 μ M protein N-

linked Hcy and 5.4 2.5 μ M tHcy [297]. Human milk contains 0.28 0.09 μ M

(n ¼ M tHcy. The presence of protein N-linked

Hcy has not been previously described in milk or other foodstuffs, but the levels of
tHcy in milk are comparable to tHcy levels reported for other foodstuffs examined
thus far (Roquefort cheese, white bread, tuna, and pig liver; [307]).

3) protein N-linked Hcy and 2.3 μ

5.2.1.5 Hair Keratin

Human and animal hair keratin contains significant amounts of N-linked Hcy [308].
Normal human hair contains 82-95 pmol N-Hcy/mg hair (Table 5.8 ). N-linked Hcy
comprises 31-36 % of all Hcy content in human hair keratin, while the remaining
64-69 % is S-linked. Similar levels of N-Hcy-keratin are present in mouse pelage
hair (Table 5.9 ). Other mammalian species examined, such as the rat, the rabbit, the
dog, the cat, the goat, the sheep, and the horse, all contain N-Hcy-keratin in their
hair. N-Hcy-keratin is also present in feathers of birds, such as chicken, pigeons,
and sea gulls.
More N-Hcy-keratin accumulates in pelage hair from hyperhomocysteinemic
mice [308]. For example, N-Hcy-keratin is elevated 12-, 6.3-, or 2.7-fold in pelage
from Cbs / , Cse / ,orMthfr / mice, compared with wild-type animals, respec-
tively (Table 5.9 ). The increase in N-linked Hcy content is associated with dimin-
ished solubility of hair keratin in 2 % SDS, most pronounced in Cbs / mice, in