Serine transhydroxymethylase activity in vertebrate retina.

The presence of serine transhydroxymethylase (STHM; EC 2.1.2.1) in crude homogenates of rat, guinea pig and goat retina has been demonstrated. There was a variation in the levels of retinal STHM activity in the three species. Substantial STHM activity was found in all the three retinal preparations in the absence of pyridoxal-5-phosphate in the incubation medium. There was direct correlation (r = 0.995; p less than 0.001) between the STHM activity and the glycine content in rat telencephalon, midbrain, medulla-pons, spinal cord and retina. These findings suggest that STHM is probably an important enzyme for the synthesis of neural glycine in the vertebrate retina.