Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

IV. Water-Soluble Vitamins
715
5’CH 2 OH
C
O
(HOCH) 3
HCCH 2
R
H 3 C
N
N
O
NH
N
N
CH 2
N
N
O
H 3 C
1’CH 2
CH 3
1
8 9 10 2
7
6
3
5 4 NH
N
Riboflavin O
ATP
Flavokinase
ADP
O
CH 2 OP
OH
N
O
Covalent complex of
histidine residue and FAD
NH
CH 2
OH
H 3 C
N
N
O
H 3 C
N
NH
FMN
O
ATP
P 1
Riboflavin
Phosphatase
H 3 C
(HOCH) 3
PP 1
FAD synthetase
O O
CH 2 O O OCH 2
P P
(HOCH) 3
OH
CH
OH
2
N N O
H
N
O N
H
OH OH
N
NH 2
N
H 3 C
N
NH
AMP
Pyrophosphatase
O
FAD
FMN
FIGURE 23-16 Riboflavin. The major forms of riboflavin found in cells are flavin adenine mononucleotide (FMN) and flavin dinucleotide (FAD). In
some enzymes, riboflavin may also be covalently bound to the enzymes that it serves, for example, succinic dehydrogenase.
d . Determination of Niacin Status
A nicotinamide loading test has been used to determine
niacin status of patients. The patient is given an oral dose
of nicotinamide, and the urinary excretion products, which
are species dependent, are measured. For humans, monkeys,
dogs, rats, and swine largely methylated products are
produced. Analytical approaches in measuring nicotinic
acid and niacin now involve hydrophilic interaction chromatography
or capillary electrophoresis using UV, florescence,
or mass spectrophotometry for detection ( Kirkland,
2007 ).
3 . Ribofl avin
a . Introduction
Riboflavin was one of the first of the B vitamins identified.
Riboflavin is present in tissue and cells as flavin adenine
dinucleotide (FAD) and flavin adenine mononucleotide
(FMN). FAD and FMN are cofactors in aerobic processes,
usually as cofactors for oxidases, although FAD also can
function in an anaerobic environment as a dehydrogenase
cofactor. Many flavin-containing proteins are also found in
the smooth endoplasmic reticulum of cells associated with
microsomal enzymes ( Fig. 23-16 ).