Abstract
1) Antibacterial property of modified β-lactoglobulin (β1g) and modified α-lactalbumin (α1a) in which carboxyl, amino, indol and guanidyl residues were blocked, was studied using Streptococcus lactis and Str. pyogenes. Modified proteins added to a culture of milk serum protein-free sterilized Jhey were 0.7% as protein concentration. Carboxyl residue-modified proteins (COOH-mβ1g or COOH-mα1a) showed the strongest inhibitory effect to microbal growth. Other aminoic acids residues-modified proteins did not show inhibitory effects. Unmodified β1g was somewhat effective but unmodified α1a was ineffective for both bacteria.
2) Antibacterial property of COOH-mβ1g and COOH-mα1a was stronger for Str. pyogenes than for Str. lactis.
3) The effect of COOH-mβ1g on base composition of tRNA in the body of Str. lactis was studied by ion-exchange chromatography of Dowex 1×2 Cl- type. Addition of COOH-mβ1g (0.7% as protein concentration) to a culture of Str. lactis gave a great change of base composition of uridylic acid and guanidylic acid. The ratio of purine/pyrimidine was raised.
4) By the addition of this modified protein, the intensity of fluorescence of the bacteria body was decreased: this phenomenon seemed to be due to the association between COOH-mβ1g and the bacteria bady. Ultraviolet absorption spectra of tRNA were also changed.
5) The inhibitory effect of COOH-mβ1g on microbal growth was presumed to be due to that the disclosed or the free amino residue of modified proteins was associated by ionic bond with carboxyl residue of protein in bacteria membrane and this complex prevented a transport activity of bacteria.
