1. M. Dixon and E. C. Webb, “Enzyme,” Longmans, Green Co., 1962, p. 327.
2. K. Iwai, M. Kobashi and H. Fujisawa, “Chemistry and Biology of Pteridines,” ed. by K. Iwai, M. Akino, M. Goto and Y. Iwanami, distributed by Maruzen Co., Ltd., Tokyo, 1970, p. 199.
3. T. Shiota, R. Jackson and C. M. Baugh, “Chemistry and Biology of Pteridines,” ed. by K. Iwai, M. Akino, M. Goto and Y. Iwanami, distributed by Maruzen Co., Ltd., Tokyo, 1970, p. 265.