12
chapter 1
Water, Acids, Bases, and Buffers
FIGURE 1-10
The 'H-NMR pattern
{in vitro,
600 MHz) of cerebrospinal fluid (CSF) of a patient with creatine deficiency syndrome
(a) compared with normal CSF (b). Note the near absence of creatine and creatinine in the patient’s CSF. The
ethosuximide observed in the patient’s CSF is a drug used in antiepileptic therapy. [Reproduced with permission from
A. Schulze et ah, Creatine deficiency syndrome caused by guanidinoacetate methyltransferase deficiency: diagnostic
tools for a new inborn error of metabolism.
J. Pediatr.
131, 626 ( 1997).]
under investigation. Determining the area under the NMR
spectrum for a given compound provides a measure of the
number of nuclei that are polarized by the magnetic field,
and the relative abundance of different nuclei in tissues
can be measured.
Atomic nuclei suitable for biological studies include
'H,
13
C,
15
N, l
9
F,
2 3
Na,
3 1
P, and
3 9
K. Determination of
intracellular pH utilizes
3 1
P-NMR because the resonance
frequency of inorganic phosphate
(Pj)
varies predictably
with changes in pH. The exact location of the Pj sig-
nal depends on the relative concentrations of H
2
PO
4
and
HPO2-, which in turn depend on the intracellular pH and
pK' of inorganic phosphate under physiological condi-
tions. Thus, the position of the Pj signal in the NMR
spectrum provides a measure of intracellular pH. Apart
from measurements of H+ concentrations in several tis-
sues under varying physiological conditions, NMR anal-
ysis of muscle tissues in a patient’s forearm has been
used to diagnose a hereditary defect in the breakdown of
muscle glycogen (
McArdle’s syndrome).
In normal indi-
viduals during exercise, glycogen in the muscle breaks
down to lactic acid, thus decreasing the pH. However,
in patients with McArdle’s syndrome, the pH does not
change with exercise because glycogen is not catabo-
lized to lactic acid (Chapter 15). *H- and
3
IP-NMR spec-
troscopy has been used to measure metabolically signifi-
cant components in tissues and fluids, including brain and
cerebrospinal fluid. In a 4-year-old female patient with a
defect in creatine formation due to a deficiency of guani-
dinoacetate methyltransferase, phosphocreatine synthesis
is severely diminished in many tissues including the brain
(Figure 1-9). Determination of creatine and creatinine in
cerebrospinal fluid by NMR can be used to diagnose
cre-
atine deficiency syndrome
(Figure 1-10). Creatinine is an
end product of creatine and phosphocreatine (Chapter 17).
The phosphocreatine pool is essential for the storage and
transfer of energy via high-energy phosphate compounds
(ATP). In this patient who exhibited dystonic-dyskinetic
syndrome, seizures, and psychomotor retardation, NMR
spectroscopy revealed a depletion of creatine, phosphocre-
atine, and accumulation of guanidinoacetate (Figure 1-10).
Oral
administration
of creatine
resulted
in
clinical
improvement.
High-quality anatomical cross-sectional images can be
produced by the use of tomographic methods with NMR
instead of x-rays as a probe. Magnetic resonance images
