Amgen (United States)
Publishes on Muscle metabolism and nutrition, Circadian rhythm and melatonin, Diet and metabolism studies. 8 papers and 564 citations.
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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.
Blood was collected at intervals during a 24-hour period from 23 healthy male volunteers on diets containing various amounts of protein; the plasma was assayed for 16 amino acids. Among subjects receiving 0.71 or 1.5 gm of protein per kilogram of body weight, the concentrations of tyrosine, phenylalanine and tryptophan tended to be lowest at 2:00 and highest at or after 10:30 a.m. Volunteers given a diet containing less than 0.04 gm of protein per kilogram showed similar fluctuations in the concentrations of the above amino acids and methionine, but peak plasma levels were observed somewhat earlier in the morning. All the amino acids studied showed some tendency to vary with time of day. Tyrosine, tryptophan, phenylalanine, methionine, cysteine and isoleucine underwent the greatest per cent changes; the amino acids whose plasma concentrations were highest (that is, alanine, glycine and glutamic acid) showed the least tendency to vary.
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.
Production and properties of glucose isomerase from a Co2+-sensitive Streptomyces species were studied. After 4 days of shaking cultivation at 30 degrees 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 of 0.5 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 degrees C, respectively. The Michaelis constant for fructose was 0.40 M. Mg2+ was found to enhance the glucose isomerase activity, whereas the effect of Co2+ 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 70 degrees C.