Table 2. Model Parameters used in the model outlined in Fig 2 and simulated in Fig 3.

Reaction	kon[a]	koff	kcat	KD or KM	Note
E+S = ES	1e7	3680		368 μM	[b]
ES-> E+P			25.5		[b]
B+G = BG	1e7	0.4		40 nM	[c]
BG+G = BGG	1e7	6		0.6 μM	[d]
BGG-> BG+E			0.1		[d]
G+F = GF	1e7	60		6.0 μM	[e]
F+BG = FBG	1e7	60		6.0 μM	[e]
GF+BG = GFBG	1e7	2.5		0.25 μM	[f]
G+FGB = GFBG	1e7	2.5		0.25 μM	[f]
GFBG->E+FBG			1.8		[g]
E+F = EF	1e7	5		5 μM	[h]
B+E = BE	1e8	0.01		0.1 nM	[i]
F+BE = FBE	1e7	60		6.0 μM	[e]
G+FBE = GFBE	1e7	0.5		50 nM	[j]
GF+BE = GFBE	1e7	0.5		50 nM	[j]
GFBE->E+FBE			1.8		[k]
BE+G = BEG	1e7	3		0.3 μM	[l]
BEG->BE+E	1e7		0.1		[l]

Abbreviations used are: plasmin (E), S-2251 (S), pNA (P), SK (B), Pgn (B), Fgn (F).

[a] association rate constants approximated to 10⁷ M^-1s^-1 at 37°C. Values for SK•Pgn complex formation in line k_on values of around 10⁶ M^-1s^-1 from Biacore measurements at 25°C in [5, 36] and higher estimates for SK•Pm formation in [13].

[b] See Table 1

[c] 40 nM K_D is within the range in [5] or 6 nM from [13].

[d] Derived from fitting of Michaelis Menten curves without Fgn, SK•Pgn + Pgn K_M = 0.6 μM, k_cat = 0.05, This is lower than Boxrud and Bock [14] by ~ 7 fold for rSK-H46A as expected since rSK-M1GAS will be less effective without Fgn (K_M was 0.27 μM and k_cat 0.31 for Lys-Pgn in [14]). For reaction of SK•Pm we reduced K_M by half to 0.3 μM, kept k_cat same, so modest increase in activity similar to 1.5 fold improvement in [35].

[e] Upper limits of K_D for Fgn Lys-Pgn binding 8.3 μM [37], or an estimate of 0.23 μM from [38].

[f] Starting estimate from Michaelis-Menten fits (as in [c]) at each Fgn concentration. Table 1 suggests Fgn can affect K_M and k_cat, but fits indicate more change to V_max (and k_cat) (see [e]).

[g] The k_cat for this reaction accounts for most stimulation by Fgn. To achieve 30 fold stimulation of rate by Fgn k_cat increased from 0.1 [d] to 1.8 s^-1 (additional stimulation from small improvement in K_M to 0.25 from 0.6 μM).

[h] Initial estimate based on based on value in [39], but that assumed simple competitive inhibition, which is not the case as seen in Table 1.

[i] This binding of Pm to SK for SK•Pm, tighter than K_D for SK•Pgn, similar to biacore data around 0.5 nM for a number of complexes in [5] or 0.3 nM in [13] and is explained in part by increased k_on e.g. [13].

[j] Increase in efficiency of SK•Pm over SK•Pgn due to K_M only, in line with Table 1, which is improved from 0.6 μM to 50 nM i.e. 12-fold. This difference important for degree of curvature required to match shapes of curves in Fig 3.

[k] There is no change in k_cat, 1.8 s^-1, only change in K_M for SK•Pm vs SK•Pgn.

[l] Small improvement without Fgn of SK•Pm vs SK•Pgn activity is due to decrease in K_M (from 0.6 to 0.3 μM), in line with Table 1 data.