For chemotherapeutic antifolates used for cancer, loss of RFC expression or synthesis of mutant RFC protein with impaired function results in antifolate resistance due to incomplete inhibition of cellular enzyme targets and low levels of substrate for polyglutamate synthesis.
Two challenges often encountered in these endeavors are the transient nature of the interaction between substrates and degradation components, and low levels of substrate expression in vivo.
This mechanism allows the cells to maintain their growth rate for about one more generation in which they are able to utilize low levels of substrate.
We also detail the conditions in which robustness breaks down, such as extreme values of the input ADP, or ultra-low levels of substrates or proteins.
While a normal, albeit low, level of substrate reduction occurs under these conditions, the MoFe-protein undergoes a complex transformation; initially, the enzyme is reversibly inhibited for substrate reduction at pH 9.5, yet in a second, slower process, the MoFe-protein becomes irreversibly inactivated as measured by substrate reduction activity at the optimal pH of 7.8.
Experiments can also test the breakdown of robustness predicted at extreme light levels and very low levels of enzyme or substrates.
We hypothesized that NOS substrate levels are low in patients with severe sepsis and that low levels of the NOS substrate citrulline would be associated with end organ damage including ARDS in severe sepsis.
SlGOMT2 had low levels of activity with several substrates, including guaiacol (Table 1) and a Km value for guaiacol, 501 μM, that is 51-fold higher than that of SlGOMT1 (Table 2), resulting an enzyme that is 31-fold less efficient with guaiacol than SlGOMT1 (Table 2).
Using the N169-V152 anD184-V15252 Tev-mTALENs that more accurately mimic the cTALEN architecture, we observed no more than background activity on the nptIIΔCS substrate and, furthermore, only low levels of activity on the wild-type nptII substrate compared to the native td 15-bp substrate.
For example, recently Lumjuan et al. [ 28] have shown that the GST responsible for DDT resistance, GSTE2, has very low levels of activity against the model substrate CDNB used to detected GST-based resistance mechanisms.
With the Jurkat cell line, which demonstrated low levels of general KDAC activity, the KDAC2 substrate S7 was most efficiently deacetylated, whereas the other three substrates exhibited minimal deacetylation.
