Catalyzes the last step of the oxidative degradation of choline to glycine. Converts sarcosine into glycine. (6S)-5,6,7,8-tetrahydrofolyl-(gamma-L-Glu)(n) + H(+) + oxidized [electron-transfer flavoprotein] + sarcosine = (6R)-5,10-methylenetetrahydrofolyl-(gamma-L-Glu)(n) + glycine + reduced [electron-transfer flavoprotein] Binds 1 FAD covalently per monomer. Amine and polyamine degradation; sarcosine degradation; formaldehyde and glycine from sarcosine: step 1/1. High levels in liver, lung, kidney, thymus and oviduct, and intermediate levels in the prostate, seminal vesicle, cardiac muscle and neuro-intermediate pituitary lobe. Also expressed in pancreas and adrenal gland. Belongs to the GcvT family.