PYCR1 and neoplasm: In accordance, it is reported that PYCR1 activity plays an indispensable role in the TCA cycle sustaining under hypoxia in an NADH oxidation-dependent manner, which in principle compensates for the impaired electron entry of NADH into electron transfer chain (ETC) that utilizes oxygen as the terminal acceptor; in turn, PYCR1 activity is demonstrated to be essential for the tumor cells proliferation under hypoxia.