Fig. 6.5. Lineweaver-Burk plot
showing the oxidation rate of
LYA-lysine by Cocco II (Pleurochrysis carterae) before (circles)
and after (squares) addition of
a mixture of 0.5 f1M L-alanine
and 0.5 f1M L-isoleucine.11 v,
reciprocal of rate of oxidation of
LYA-lysine (nMmin- l ) and II S,
reciprocal of concentration of
LYA-lysine (nM). Coefficient of
variation (CV) for each point is
2-10%. Equations for the uninhibited and inhibited cases are
11 v= 191.1 (II s) + 1.7, r2= 0.98
and 11 v = 1165.9 (11 s) + 1.5,
? = 0.98, respectively (reprinted
from Pantoja and Lee 1994, with
permission from ASW)
6.2.2
[J
o
I
:E
c
c
§
:.
25
20
15
0.Q1
inhibited
uninhibited
0.02
' /S (nM-l)
0.03
LYA-Iysine as Substrate for Cell Surface Deaminases in Sea Water
S. Pantoja
0.04
In a typical experiment, a water sample is amended with LYA-Iysine. Monitoring of the
progress of the reaction shows the disappearance of the substrate and the production
of the oxidation product (LYA-E-amino-a-ketocaproic acid) (Fig. 6.6). No oxidation was
detected when the probe was incubated in 0.2 flm-filtered culture medium, confirming that oxidation was associated with particles and not with free dissolved enzymes.
The absence of cross-membrane transport of the probes was demonstrated by mass
balance of the fluorescent analogs in the dissolved fraction during the incubation.
Other reactions that remove amino acids from sea water give rates of similar magnitudes (Table 6.1, Pantoja and Lee 1994). During summer 1993, experiments showed
that deamination can account for 20% of the microbial removal of amino acids from
sea water. During winter 1992, no deamination was detected.
Pantoja and Lee (1994) explored the potential environmental control of extracellular activity by surveying activity under different temperature regimes. Again, experiments carried out during winter showed no detectable oxidation of LYA-Iysine. Oxidation occurred only in the summer in waters above 22°C (Fig. 6.7). Palenik and Morel
(1990b) found that only certain species of cultured phytoplankton possess oxidative
capacity. Thus, species succession in the planktonic community due to seasonal and
temperature changes are most likely triggering the change in oxidative activity.
The other factor that may affect oxidative deamination could be enzymatic induction, when ammonium is depleted in the medium. Palenik and Morel (1990a) detected
higher rates when cultured phytoplankton cells were growing under nitrate, but no
activity was detected when they were growing under ammonium. Ammonium is thought
to be taken up preferentially over nitrate (presumably because the first intracellular
showing the oxidation rate of
LYA-lysine by Cocco II (Pleurochrysis carterae) before (circles)
and after (squares) addition of
a mixture of 0.5 f1M L-alanine
and 0.5 f1M L-isoleucine.11 v,
reciprocal of rate of oxidation of
LYA-lysine (nMmin- l ) and II S,
reciprocal of concentration of
LYA-lysine (nM). Coefficient of
variation (CV) for each point is
2-10%. Equations for the uninhibited and inhibited cases are
11 v= 191.1 (II s) + 1.7, r2= 0.98
and 11 v = 1165.9 (11 s) + 1.5,
? = 0.98, respectively (reprinted
from Pantoja and Lee 1994, with
permission from ASW)
6.2.2
[J
o
I
:E
c
c
§
:.
25
20
15
0.Q1
inhibited
uninhibited
0.02
' /S (nM-l)
0.03
LYA-Iysine as Substrate for Cell Surface Deaminases in Sea Water
S. Pantoja
0.04
In a typical experiment, a water sample is amended with LYA-Iysine. Monitoring of the
progress of the reaction shows the disappearance of the substrate and the production
of the oxidation product (LYA-E-amino-a-ketocaproic acid) (Fig. 6.6). No oxidation was
detected when the probe was incubated in 0.2 flm-filtered culture medium, confirming that oxidation was associated with particles and not with free dissolved enzymes.
The absence of cross-membrane transport of the probes was demonstrated by mass
balance of the fluorescent analogs in the dissolved fraction during the incubation.
Other reactions that remove amino acids from sea water give rates of similar magnitudes (Table 6.1, Pantoja and Lee 1994). During summer 1993, experiments showed
that deamination can account for 20% of the microbial removal of amino acids from
sea water. During winter 1992, no deamination was detected.
Pantoja and Lee (1994) explored the potential environmental control of extracellular activity by surveying activity under different temperature regimes. Again, experiments carried out during winter showed no detectable oxidation of LYA-Iysine. Oxidation occurred only in the summer in waters above 22°C (Fig. 6.7). Palenik and Morel
(1990b) found that only certain species of cultured phytoplankton possess oxidative
capacity. Thus, species succession in the planktonic community due to seasonal and
temperature changes are most likely triggering the change in oxidative activity.
The other factor that may affect oxidative deamination could be enzymatic induction, when ammonium is depleted in the medium. Palenik and Morel (1990a) detected
higher rates when cultured phytoplankton cells were growing under nitrate, but no
activity was detected when they were growing under ammonium. Ammonium is thought
to be taken up preferentially over nitrate (presumably because the first intracellular