Influence of protease-hide protein affinity on enzymatic unhairing efficacy

To systematically investigate the catalytic mechanisms underlying enzymatic unhairing in leather processing, Michaelis-Menten kinetics was employed to quantitative profile specificity of proteases towards key hide structural proteins (keratin, collagen, elastin). The correlations between protease affinities and unhairing performance were established by the evaluations of proteases penetration in hide, the hydrolyzations of the proteins, unhairing efficiency and leather qualities. The results demonstrated that when a protease exhibited a significantly higher affinity for collagen (Michaelis constant (Km): 6.6 mg/mL) than for keratin (Km: 31.0 mg/mL) and elastin (Km: 50.9 mg/mL), it preferentially targeted collagen in the hide. This affected the destruction of the epidermis and impeded the rapid permeation of the enzyme, which was the main factor leading to a low unhairing efficiency and grain damage. Selecting a protease with a high affinity for keratin (Km: 20.8 mg/mL), a comparable degree of affinity for collagen (Km: 22.0 mg/mL), and a low affinity for elastin (Km: 47.3-54.4 mg/mL) was found to enhance enzyme permeation and unhairing efficiency, prevented grain damage, and improved leather quality. Furthermore, the affinity of protease for elastin was shown to significantly influence the permeation rate of enzyme, which was primarily associated with the looseness of leather grain. These findings establish that selecting proteases with high keratin affinity, moderate collagen affinity, and low elastin affinity is the key criterion for efficient and non-damaging enzymatic unhairing.