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absolute difference between the theoretical and experimental
14
C-
incorporation of
P
into
B
during time interval
x
In this manner, when pathway I is operational, i.e. when the experimental (Exp)
and theoretical (
Q
Bx
)
14
C-incorporations into B are of equal magnitude, then, as
expected
,
Eq. (
3.104
) returns a value of 100 % for the percent contribution of
compound
A
to the formation of compound
B
.
|Exp -
Q
Bx
|
¼
3.9.4 Sample Calculation
The following sample calculation was excerpted from Table II of (Tripathy and
Rebeiz
1988
). The purpose of the calculations was (a) to determine whether
pathway II was operational in greening barley seedlings, and (b) if it was opera-
tional to determine the extent of the contribution of
A
to the formation of
B
. In this
particular case the parameters of Eq. (
3.101
) represented the following:
P
14
C-
¼
δ
-aminolevulinic acid
A
¼
Divinyl protochlorophyllide (DV Pchlide)
Monovinyl protochlorophyllide (MV Pchlide)
The rise in specific radioactivity of DV Pchlide was a linear function of time
(Tripathy and Rebeiz
1988
).
Under these conditions, for the time interval
t
2
-t
4
, Eq. (
3.101
) assumes the
following form:
B
¼
Q
B
4
¼ð
Y
A
2
þ
Y
A
4
Þ=
2
ðΔ
B
4
Þ
(3.105)
where:
Y
A2
,Y
A4
¼
the specific radioactivity of DV Pchlide by the end of time interval
t
1
-t
2
and
t
2
-t
4
, respectively, amounted to 163 and 418 dpm/pmol, respectively
(
Δ
B
4
)
¼
the increase in MV Pchlide by the end of time interval
t
2
-t
4
amounted to
1,490 pmol
Exp
the experimental
l4
C-incorporation into MV Pchlide by the end of time
interval
t
2
-t
4
amounted to 1346.5
¼
10
3
dpm.
the theoretical
14
C-incorporation into MV Pchlide by the end of time
interval
t
2
-t
4
, as calculated from Eq. (
3.105
), amounted to 432.8
Q
B4
¼
10
3
dpm.
Since the theoretical (
Q
BX
) and experimental (Exp)
14
C-ALA incorporations into
MV Pchlide were drastically different, it was concluded that pathway I was Not
operational in greening barley seedlings. On the other hand, since in vitro
incubations exhibited a strong conversion of DV Pchlide to MV Pchlide, it was
concluded that MV Pchlide was formed from
δ
-aminolevulinic acid in vivo via
pathway II instead of pathway III.
Finally, the maximum possible percent conversion of DV Pchlide to MV Pchlide
during time interval
t
2
-t
4
was calculated from Eq. (
3.103
):
% conversion
¼
100-[(|1346.5
432.8|)/1346.5]100
¼
32 %
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