The influence of D-amphetamine on rat brain striatal reduced biopterin concentration.

Rat brain striatal reduced biopterin (BH4) levels vary diurnally by 2-fold, oscillating around a concentration of 3 micrometer. D-Amphetamine consistently induced a decrease in BH4 levels that did not exceed 25 to 30% with increasing doses; recovery of control levels required several hours. A large number of other psychotropic drugs, including other stimulants and phenylethylamine congeners, failed to induce a similar change. The amphetamine effect was blocked by methylphenidate and reserpine. The prolonged time for BH4 recovery could be explained by an amphetamine-induced functional uncoupling of quinonoid dihydropteridine reductase from striatal tyrosine hydroxylase as reported for various cofactor analogs, leading to spontaneous isomerization of the partially reduced pterin to its nonquinonoid form, which is not a substrate for the BH4 regenerating enzyme. If relevant to dopamine biosynthesis, such an uncoupling phenomenon might account for a unique neuropharmacology of the postamphetamine state.

Enzymes regulating glycogen metabolism in swine subcutaneous adipose tissue. II. Glycogen synthase.

Glycogen synthase from swine adipose tissue was purified to apparent homogeneity using ethanol precipitation, DEAE chromatography, and affinity chromatography utilizing glucosamine 6-phosphate as the ligand. The purified enzyme migrated as a single protein component during electrophoresis on polyacrylamide gels at pH 7.3 although some protein failed to enter the running gel. Enzyme incubated with sodium dodecyl sulfate (SDS) migrated as one component (mol wt similar to 90,000) on SDS-polyacrylamide gel electrophoresis. The enzyme was relatively unstable at all stages of the purification procedure, but stability was increased in the presence of glucose 6-phosphate, UDPG, or glycerol. The isoelectric point of the purified enzyme and of enzyme activity in crude homogenates was pH 4.8. The sedimentation coefficient of the enzyme in crude homogenates was 8.5 S. The pH-activity profile showed an optimum at pH 7.8 in the absence of glucose 6-phosphate but no definable optimum between pH 7.0 and 9.2 in its presence. The Km of glycogen synthase I for UDPG was 250 muM in the absence and 37 muM in the presence of glucose 6-phosphate; the K-a for glucose 6-phosphate was 18 mu-M. The K-m of glycogen synthase D for UDPG was 130 mu-M in the presence of glucose 6-phosphate; the Ka for glucose 6-phosphate was 1 mM. The anions sulfate and phosphate activated the enzyme when assays were performed in the absence of glucose 6-phosphate. Fluoride produced activation of enzyme assayed either in the presence or in the absence of glucose 6-phosphate.