Figure 4

(a) Representative spectra showing the effect of salt stress (15% NaCl) on the mycelial peptidyl-prolyl cis–trans isomerase (PPIase) activity of Penicillium oxalicum at 4, 7 and 10 days after inoculation (DAI). The PPIase activity in the crude mycelial extracts was estimated by studying the rate of chymotrypsin catalyzed cleavage of the test peptide, and expressed as the first-order rate constant, k (s^–1). Higher first-order rate constant signified greater PPIase activity in the extract. 20 μg of total proteins was used for this assay, with bovine serum albumin (BSA) as a negative control. The cyclophilin- and FK506-binding protein (FKBP)-associated PPIase activity was estimated by the extent of inhibition in the presence of 100 nM cyclosporin A (CsA) and 2 μM FK506, respectively. Control refers to the cultures grown in Sabouraud medium without supplementing with NaCl. (b) Changes in the total PPIase activity (nmol/sec/g fresh weight mycelium) and (c) specific PPIase activity (nmol/sec/mg total proteins), and (d) total soluble proteins (mg/g fresh weight mycelium) in the mycelia of Penicillium oxalicum grown in the presence or absence of salt. (e) Effect of specific inhibitors of cyclophilins (CsA) and FKBPs (FK506) on mycelial PPIase activity. The percent inhibition of PPIase activity is expressed with respect to the uninhibited control. The values depict the mean of three biological replicates ± standard error and are significant at P ≤ 0.001 (Tukey-HSD test; α = 0.05). The values with distinct letters are significantly different. (DAI: days after inoculation).