  A protein undergoes conformational dynamics with multiple time scales, which
results in fluctuating enzyme activities. Recent studies in single molecule
enzymology have observe this "age-old" dynamic disorder phenomenon directly.
However, the single molecule technique has its limitation. To be able to
observe this molecular effect with real biochemical functions {\it in situ}, we
propose to couple the fluctuations in enzymatic activity to noise propagations
in small protein interaction networks such as zeroth order ultra-sensitive
phosphorylation-dephosphorylation cycle. We showed that enzyme fluctuations
could indeed be amplified by orders of magnitude into fluctuations in the level
of substrate phosphorylation | a quantity widely interested in cellular
biology. Enzyme conformational fluctuations sufficiently slower than the
catalytic reaction turn over rate result in a bimodal concentration
distribution of the phosphorylated substrate. In return, this network amplified
single enzyme fluctuation can be used as a novel biochemical "reporter" for
measuring single enzyme conformational fluctuation rates.
