Biomedical Engineering Reference
In-Depth Information
detailed description on the biosynthesis of γ-PGA has been well reviewed [5,8,14,15,41,43],
and an elaborate discussion here is beyond the scope of this chapter.
O
OH
O
OH
O
H
β
α
γ
OH
N
*
*
*
N
H
2
N
H
O
O
OH
O
n
(A)
O
O
H
H
N
N
*
*
-
-
H
+
H
2
+
COO M
COO (M )
½
n
n
(B)
(C)
Figure 1. The chemical structure of poly(γ-D,L-glutamic acid) and poly(γ-glutamates). (A) H-form of γ-
PGA; (B) monovalent metal salt form of γ-PGA; (C) divalent metal salt form of γ-PGA; M
+
= Na
+
, K
+
or NH
4
+
; M
2+
= Ca
2+
or Mg
2+
; Greek symbols (α, β, γ) denote carbon positions; Asterisk (*) symbol
indicate the chiral carbon atom.
2.2. Physico-chemical Properties
The γ-PGA biosynthesized from
B. subtilis
(natto) was characterized for various physical
and chemical properties by using several instrumental techniques including Fourier transform
infrared spectrophotometry (FT-IR),
1
H- and
13
C-nuclear magnetic resonance spectroscopy
(
1
H- and
13
C-NMR), differential scanning calorimetry (DSC) and thermal gravimetric
analysis (TGA), and the results are furnished in Table 2 [15]. Elemental analysis of purified
H-form of γ-PGA at 1.23 x 10
6
kDa (C: 44.86%; H: 5.91%; N: 10.49%; S: 0%) was in close
agreement with the calculated values (C: 46.51%; H: 5.43%; N: 10.85%; S: 0%) based on the
formula composition [15]. The viscosity of γ-PGA was reported to be strongly dependent on
pH, γ-PGA concentration, temperature and ionic strength [15,44], which should be due to the
abrupt changes caused by these parameters on the conformation of γ-PGA. The viscosity of
4% Na-γ-PGA solution at 25°C increased following a rise in pH and γ-PGA dose, but
decreased with temperature and ionic strength [15]. The γ-PGA remained unaltered on
heating at 80°C for 60 min, however, it was rapidly hydrolyzed at 120°C because of random
chain scission [33].
