RESULTS
Formation of asparaginase II in standing cultures.
Schwartz et al. (26) observed that asparaginase
II was formed in standing cultures during
the transition from aerobic to anaerobic growth.
The time course of the appearance of the enzyme
under these conditions is shown in Fig. 1. Little
enzyme was produced by cells during aerobic
growth. As soon as the aeration was discontinued,
the specific activity increased exponentially
until a plateau was reached by 40 min. The
form of these kinetics suggested that a factor,
perhaps oxygen, inhibitory to the production
of the asparaginase was disappearing during
the period following the cessation of aeration.
These considerations led us to study the formation
of enzyme under strict anaerobiosis.
It was important to establish beforehand that
the enzyme is stable under aerobic conditions.
Sulfhydryl reagents did not affect the enzyme in vitro. Incubation of asparaginase at pH 8
with 10 mm p-hydroxymercuribenzoate or with
any of the alkylating agents, iodoacetate, iodoacetamide,
or N-ethylmaleimide, also at 10 mM,
did not inhibit the enzyme. Asparaginase II
was not inactivated by exposure to air. When
the bacteria were aerated after a period of anaerobic
growth, the formation of the enzyme stopped.
Even so, enzyme previously formed in the absence
of air remained at a constant concentration
in the aerated culture.