the two metals: 10.0 kJ/mol for tungsten and 10.5
kJ/mol for molybdenum. Apparently the affinity for the
electrode surface is not much different for tungsten
and molybdenum. The chlorate catalysis, however, is
much faster with molybdenum than with tungsten.
The higher catalytic response for molybdenum is probably
due to kinetic factors, because a faster catalysis
for tungsten is expected based on the reduction potential
(23). The reduction potential for the molybdenum
complex was found to be 500 mV higher than for tungsten.
It is a common finding that tungsten compounds
are more slowly reduced than their molybdenum counterparts
(24). This is the first report of an electrochemical
method to determine the molybdenum and tungsten
content of a protein. It is also the most sensitive
determination described to date. Furthermore, tungsten
and molybdenum can be determined in the presence
of a high excess of other biochemically important
metals, such as iron.