No abstract

The intraperitoneal administration of melatonin to rats caused an increase in brain serotonin concentration, especially in the midbrain. This effect could be demonstrated within 20 minutes of melatonin administration and was not associated with changes in norepinephrine concentration.

The concentration of tyrosine in the plasma of normal males varies diurnally. It is lowest (9.5 +/- 0.35 micrograms per milliliter) between 0130 and 0230 hours and rises to a peak of 16.2 +/- 0.82 micrograms per milliliter by 1030 hours. This rhythm persists when subjects are maintained for 2 weeks on a diet that is very low in protein.

No abstract

Production and properties of glucose isomerase from a Co2+-sensitive Streptomyces species were studied. After 4 days of shaking cultivation at 30°C and 200 rpm, a maximum of 1.1 enzyme units per ml of broth was obtained. Cell-free glucose isomerase, obtained from mycelia heat-treated in the presence of0.5 mM Co2+, showed a 3.5-fold increase in specific activity over enzyme obtained from untreated mycelia. The optimum pH and temperature for the glucose isomerase were 7 to 8 and 80°C, respectively. The Michaelis constant for fructose was 0.40 M. Mg2+ was found to enhance the glucose isomerase activity, whereas the effect of C02+ on enzyme activity depended on the manner in which the enzyme was prepared. This glucose isomerase was quite heat stable, with a half-life of 120 h at 700C.