CcO activity was significantly higher in COX4-1-overexpressing glioma cells (1728.0 ± 131.7 nmol/sec/mg and 1460.0 ± 51.3 nmol/sec/mg in COX4-1-U251 clones versus 316.5 ± 11.0 nmol/sec/mg and 236.9 ± 28.8 nmol/sec/mg in vector-U251 clones; 3087.0 ± 290.7 nmol/sec/mg and 2220.0 ± 204.5 nmol/sec/mg in COX4-1-D456 clones versus 663.6 ± 68.2 nmol/sec/mg and 581.0 ± 42.78 nmol/sec/mg in vector-D456 clones; p <0.0001; Fig. 5B). Here, COX4I1 is linked to central nervous system cancer.