considered important at 60 [tM as substrate saturating conditions were maintained

throughout the duration of the run. However, at higher substrate concentrations, such as

500 lM, incubation time does appear to influence the determination of activity (Fig 2-la

& 2-1b). At 500 [aM, incubation times exceeding approximately 80 minutes for Fl and

120 minutes for U3 would be necessary in order to resolve positive activities at both sites.

Phosphatase

 Mean activities for Fl and U3 sites were 3717 and 5433 (unitless) with standard

errors 2.5% and 5.0% of the mean at 500 [aM, respectively (Figures 2-2a & 2-2b).

Relative differences between sites substantially decreased at concentrations at or above

250 [aM. In contrast to the MUF-cellobioside assay, high concentrations did not result in

erratic behavior over the incubation period but rather remained linear (Figures 2-2a & 2-

2b). The lowest concentration of 5 [aM exhibited very linear relationships over time in all

replicates in both nutrient conditions. Mean activity values were 287 and 4050 with

standard errors 6.5% and 1.2% of the mean for the Fl and U3 sites, respectively. The

low activity at the Fl site reflected the need for a higher substrate concentration in order

to counteract potential interference in future experimental runs where microbial

phosphatase production may be lower.

 The most appropriate concentration for the purpose of future studies was

determined to be in the 50 [aM range (Figure 2-2c), before a substantial decrease in

activity occurred in the U3 sample. Linear responses occurred in both the Fl and U3

samples over the length of the incubation period with mean activity values of 2770 and

9067 with standard errors 2.5% and 2.9% of the mean, respectively. These values reflect

the highest activity value while still minimizing laboratory error. Incubation time at 50

[aM does not appear to be an important consideration since linear relationships were