PURIFICATION OF MOUSE BRAIN PHOSPHOSERINE PHOSPHOHYDROLASE AND PHOSPHOTRANSFERASE

Mouse brain phosphoserine phosphatase (EC 3.1.3.3.) that has been partially purified 150-fold or greater tolerates heating at 52 ° for several hours, resulting in a preparation that is 1200- to 1500-fold enriched over an aqueous homogenate of brain. Sucrose-gradient centrifugation of the purified enzyme shows one symmetrical peak of activity, with an estimated molecular weight of about 47,000. The enzyme, which underwent prolonged heating during purification, retains its sensitivity to inhibition by l-serine. However, the degree of inhibition is dependent upon the incubation temperature, with elevated temperature decreasing the effectiveness of serine as an inhibitor. The inhibition by serine of the phosphohydrolysis of phosphoserine is compatible with an ordered release of products, with serine released first. The enzyme also catalyzes a phosphoryl group transfer from phosphoserine to serine. Preliminary analysis of this activity is also consistent with a mechanism whereby there is an ordered product release. © 1969.