Melatonin immunoreactivity in the photosynthetic prokaryote Rhodospirillum rubrum: implications for an ancient antioxidant system.

Rhodospirillum rubrum is a spiral anoxygenic photosynthetic bacterium that can exist under either aerobic or anaerobic conditions. The organism thrives in the presence of light or complete darkness and represents one of the oldest species of living organisms, possibly 2-3.5 billion years old. The success of this prokaryotic species may be attributed to the evolution of certain indole compounds that offer protection against life-threatening oxygen radicals produced by an evolutionary harsh environment. Melatonin, N-acetyl-5-methoxytryptamine, is an indolic highly conserved molecule that exists in protists, plants, and animals. This study was undertaken to determine the presence of an immunoreactive melatonin in the kingdom Monera and particularly in the photosynthetic bacterium, R. rubrum, under conditions of prolonged darkness or prolonged light. Immunoreactive melatonin was measured during both the extended day and extended night. Significantly more melatonin was observed during the scotophase than the photophase. This study marks the first demonstration of melatonin in a bacterium. The high level of melatonin observed in bacteria may provide on-site protection of bacterial DNA against free radical attack.

Stimulation by 3-mercaptopicolinate of net glucose uptake by perfused livers from diabetic rats.

Glucose uptake/production was studied as a function of varied glucose loads in isolated perfused livers from glucagon-treated alloxan-diabetic rats. Uptake of D-[U-14C]glucose was seen at all levels studied - 9.5-71 mM. In studies with unlabelled D-glucose carried out in the absence of 3-mercaptopicolinate, livers of diabetic rats showed a net production of glucose with perfusate glucose levels less than 22 mM. Above this level, these livers exhibited a time- and concentration-dependent net uptake of glucose for a period of 20-30 min. When 4 mM 3-mercaptopicolinate, which inhibited gluconeogenesis from endogenous substrates, was included in perfusates, a continuous net uptake of unlabelled glucose was observed at all levels above 4 mM. This lowering of the null-point, cross-over glucose concentration was shown to relate mechanistically to the observed reduction in steady-state hepatic glucose 6-phosphate level produced by mercaptopicolinate. The need for supplemental mechanisms of glucose utilization by high Km hepatic enzyme(s) operative in the virtual absence of insulin-dependent glucokinase also is indicated by these observations and by kinetic analysis.