A peptide-Fe(II) complex from Grifola frondosa protein hydrolysates and its immunomodulatory activity

Grifola frondosa protein was hydrolysed using Alcalase, and the resulting hydrolysates (CGFP) were filtered using 5 and 1 kDa nominal cut-off ultrafiltration membranes and separated using Sephadex gel chromatography. Two main fractions, named GFP-1 and GFP-2 were obtained. CGFP-Fe and GFP-Fe were synthesized using ferrous chelation. Results showed that the GFP-2 fraction with molecular weight of 963 Da had the highest Fe(II) chelating activity (2680 ± 40 μg/g). UV spectrum showed that the Fe(II) shifted the maximum absorption to shorter wavelengths. The peptides measured using FTIR showed that the GFP-Fe peptide and the un-chelated peptide had different C–O and C=O absorption peaks. The effects of CGFP, CGFP-Fe, GFP2-2 and GFP-Fe on splenocytes proliferation and cytokines secretion were studied in vitro. Both the GFP-2 and GFP-Fe had good immune-enhancing activity. Furthermore, GFP-Fe showed an ability to promote the proliferation of splenocytes and peritoneal macrophages. The iron-chelating peptide of Grifola frondosa still maintained its immune enhancing activity after in vitro gastrointestinal digestion. The results suggested that GFP-Fe might be beneficial as a new iron supplement and as an immunological enhancement.