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The interactions of spermine (4+ charge at physiological pH), N1-acetylspermine(3+), spermidine(3+), N1- and N8-acetylsperimidine(2+), putrescine(2+), hexaamminecobalt(3+), and magnesium(2+) with nucleosome core particles have been examined by using thermal denaturation and circular dichroism. Tetra- and triamines were 2-3 times more effective than diamines at stabilizing core particles against thermal denaturation. Secondary effects were also observed, with acetylpolyamines slightly less effective than unmodified polyamines of equivalent charge. Hexaamminecobalt(3+) was less effective than the triamines, while magnesium had essentially no effect. This is surprising since magnesium is more effective than diamines at stabilizing naked DNA. All the cations tested altered the circular dichroism spectra of the core particles in the DNA region (284 nm). The peak at 284 nm was suppressed by tetra- and trivalent compounds to approximately twice the extent of divalent compounds. Magnesium appears to suppress the peak by a lesser extent than the diamines. This indicates that the DNA twist and/or folding is changed by these cations. A plateau of both thermal denaturation and circular dichroism effects was observed at cation concentrations where 30-40% of the total DNA negative charges could be neutralized by the added cations. We suggest that polyamine and histone acetylation function in concert to lower the stability and change the conformation of the nucleosome core, thus facilitating replication and transcription in vivo.

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Nine male marathon runners were exercised to exhaustion to determine the effects of a 27-h fast on endurance performance. Each subject completed two exercise tests at the same treadmill speed (set at 70% maximal O2 uptake), one following a 27-h fast and one 3 h after a preexercise meal, in random order. Fasting caused a 44.7 +/- 5.8% (SE) decrease in endurance performance (P less than 0.01). Blood, muscle, psychological, and ventilatory data were examined to determine the cause of the decreased performance. Fasting caused significant increases in O2 uptake (9.3 +/- 2.0%), heart rate (8.4 +/- 2.4%), and rating of perceived exertion, ventilation, and psychological fatigue, evident within the first 60 min of exercise. There were no differences in plasma glucose or epinephrine levels. Muscle glycogen degraded at the same rate (0.482 +/- 0.146 vs. 0.470 +/- 0.281 mumol.g-1.min-1 in the nonfasted and fasted tests, respectively) despite lower respiratory exchange ratio and elevated free fatty acid levels, which may partially explain the elevated O2 uptake. Lactate, insulin, and norepinephrine were all increased in the fasted test (P less than 0.05). The increase in norepinephrine (r = 0.79, P less than 0.01), the diameter of type I muscle fibers (r = 0.70, P less than 0.05), and ending insulin levels (r = -0.88, P less than 0.01) were correlated with endurance time in the fasted state. Fatigue in endurance running for 27-h fasted humans appears to be related to a combination of physiological, psychological, metabolic, and hormonal changes.

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