Effects of Cysteine and 4-Amino-1-Naphthol on Solutions of Lysosomal Enzymes Exposed to High Doses of Radiation

The effect of γ-irradiation on the lysosomal enzymes (acid phosphatase, DNase, RNase, β-galactosidase, β-glucuronidase, muramidase, and arylsulfatase) in the absence and in the presence of cysteine or 4-amino-1-naphthol (4A1N) was studied. Inactivation of these enzymes in the absence of the radioprotectors, cysteine and 4A1N, followed first-order kinetics. Muramidase was the most radiosensitive of all enzymes, having a $D_{37}$ value of 4 krads, whereas acid phosphatase was the most resistant, having a $D_{37}$ of 290 krads. Cysteine (0.1 mM) exerted no radioprotective effect on β-glucuronidase, the $D_{37}$ decreasing by 4 krads, whereas β-galactosidase was slightly protected, the $D_{37}$ increasing by 3 krads. The following enzymes were markedly protected: arylsulfatase, $D_{37}$ increased by 8 krads; muramidase, increased by 9 krads; DNase, increased by 13 krads; acid phosphatase, increased by 360 krads. Cysteine exerted some radio-protection on RNase only, with doses ranging from 5 to 10 krads. 4-Amino-1-naphthol (0.1 mM) exerted no protective effect on arylsulfatase; the $D_{37}$ decreased by 12 krads. The remaining enzymes were protected: the $D_{37}$ of acid phosphatase increased by 400 krads; β-glucuronidase, 193 krads; β-galactosidase, 148 krads; DNase, 40 krads; muramidase, 22 krads; RNase, 4 krads.