Biology Reference
In-Depth Information
Table 9.1
Nonprotein composition of axoplasm
Class
Component
mM
Amino acids
Nonpolar AA (alanine)
16.14
Polar AA (glycine)
18.41
Acidic AA (aspartate)
100.29
Basic AA (arginine)
6.06
Betaine
73.7
Taurine
106.7
Homarine
20.4
Cysteic acid
4.9
Organic metabolites
Isethionic acid
164.6
Glycerol
4.35
Others
11.02
Carbohydrates
Glucose
0.24
Mannose
0.92
Fructose
0.24
Sucrose
0.24
Inorganic ions
Potassium
344
Chloride
151.2
Sodium
35
Phosphate
17.8
Magnesium
10
Sulfate
7.5
Calcium
3.5
Nucleoside triphosphates
ATP
1
Adapted from
Deffner and Hafter (1960a, 1960b)
and
Morris and Lasek (1982)
.
Gallant, Terakawa, & Pant, 1981; Brown & Lasek, 1993
), so they are minimized in
buffer X. Extruded axoplasm placed in buffer X will retain its overall shape and or-
ganization for
24 h (
Morris & Lasek, 1982
) and will maintain fast axonal transport
>
for
3-4 h (
Brady et al., 1985, 1993
).
>
9.2
ANALYSIS OF AXOPLASMIC MICROTUBULE DYNAMICS
The stability of axoplasmic organization in buffer X provides a unique model study
of microtubule and actin dynamics
in situ
(
Morris & Lasek, 1984
). Tubulin dimers
represent 22% of total axoplasmic protein, with a concentration of approximately
25
m
M(
Morris & Lasek, 1984
). Squid microtubules resemble mammalian micro-
tubules in many ways with regard to its polymerization (although at optimal tem-
perature as 25
C) and depolymerization (by cold, Ca
2
รพ
ions, colchicine, etc.)
