Activation of the endogenous acid protease in the head of Litopenaeus vannamei induced by UV‐C irradiation

Abstract

Previous studies have found that UV-C irradiation activated endogenous acid protease (EAP) in shrimp heads. Aiming at understanding the effect of UV-C irradiation on the activation of EAP and improving the utilisation of EAP, the effect of UV-C irradiation on the enzymatic properties and conformation of EAP was investigated. The enzymatic properties of EAP were unaltered after UV-C irradiation, and the optimum pH, temperature, and NaCl concentration were 3, 60°C, and 0.5 mol/L, respectively. Ca 2+ and Mg 2+ activated the enzyme. The molecular weight of the purified endogenous acid protease (P-EAP) was 32 kDa. UV-Vis, FTIR, circular dichroism, and fluorescence spectroscopy indicated that the increase in enzyme activity by UV-C irradiation was related to an increase in tryptophan and hydrogen bonding, implying that it may be the change in the spatial structure of the protein that caused the activation of the enzyme. Results revealed that UV-C irradiation can be used to activate proteases and provide a reference for enhancing the enzymatic activity of other enzymes from shrimp heads.

Ultraviolet irradiation effect on characteristics of protease enzyme from African catfish (Clarias sp.) intestines

“…hese structural change and protein denaturation could be the reasons behind the observed decrease in EA of protease enzyme from AC intestines following UV irradiation. However, study by Cao et al (2014) and Dou et al (2023) yielded contradictory result as the EA of head shrimp protease enzyme increased after UV irradiation [11,14]. The difference nature of enzyme sources may be the underlying cause of this contrast result.…”

“…The UV irradiation treatment and crude enzyme extraction procedures were carried out based on previous studies by Cao et al (2014) and Dou et al (2023) with some modifications [11,14]. The catfish intestines were diced and chopped using a food chopper for 4 min with the addition of cool pure water (1:3 w/v).…”

“…The reaction mixture was then subjected to centrifugation at 10,000 rpm and a temperature of 4°C for 10 minutes. The content of tyrosine in the supernatant was determined using the BCA reagent [14]. Activity units (U) were defined as 1 μmol of tyrosine released from casein per minute of the reaction [4].…”

“…The crude enzyme from UV irradiated AC intestines at exposure time of 0, 10, 20 and 30 minutes was used as samples to collect of FTIR, UV-Vis and Fluorescene spectra. The protein concentration of crude enzyme extract was diluted to 100 mg/L prior to measurement [14].…”

“…Cary 60 UV-Vis (Agilent) spectrophotometer was used to measure the absorption spectra of crude enzyme extract in the region of 200-800 nm [14].…”