Table 1.

Thermodynamic Stabilities^a and Fibrillation Lag Times^b (pH 7.4 and 37 °C)

Analog	ΔGu (kcal/mol)	Cmid(M)	m(kcal/mol/M)	Fibrillation lag time (days)
Human insulin	2.4 ± 0.1	4.1 ± 0.2	0.57 ± 0.02	3.5 ± 0.6
AspB28-insulinc	2.4 ± 0.1	4.1 ± 0.1	0.60 ± 0.01	1.7 ± 0.3
KP-insulind	2.4 ± 0.1	4.1 ± 0.1	0.59 ± 0.01	2.6 ± 0.3
Human proinsulin	2.8 ± 0.1	4.0 ± 0.2	0.71 ± 0.03	15 ± 2.5
SCI-57	4.3 ± 0.1	5.5 ± 0.1	0.79 ± 0.02	>180

^aThermodynamic stabilities were inferred from CD-detected guanidine denaturation studies by application of a two-state model.³⁴ Data are obtained in part from Table 1 of Hua and colleagues.³⁴ Stability (kcal/mol) is defined as the free energy of unfolding (ΔG_u) at 37 °C as extrapolated to zero denaturant concentration;³⁸ uncertainties are ±0.1 kcal/mol. C_mid is defined as that molar concentration of guanidine-HCl associated with 50% protein unfolding. The m value (kcal/mol/M) is defined as the slope in plotting the unfolding free energy versus molar concentration of denaturant; this slope is often found to be proportional to the protein surface area exposed on unfolding.

^bFibrillation lag times were determined by ThT fluorescence following gentle agitation in the presence of an air-liquid interface as described.³⁰ Proteins were made in 60 mM PBS (pH 7.4) in the absence of zinc ions and gently rocked at 37 °C in a glass vial in the presence of an air-water interface.⁴²

^cThis analog, the active component of Novolog, contains the amino-acid substitution Pro^B28→Asp.

^dThis analog, the active component of Humalog, contains amino-acid substitutions Pro^B28→Lys and Lys^B29→Pro.