Trypanosoma brucei is the causative agent for African sleeping sickness. We have made in vitro and in vivo studies on the allosteric regulation of the trypanosome ribonucleotide reductase, a key enzyme in the production of dNTPs needed for DNA synthesis. Results with the isolated recombinant trypanosome ribonucleotide reductase showed that dATP specifically directs pyrimidine ribonucleotide reduction instead of being a general negative effector as in other related ribonucleotide reductases, whereas dTTP and dGTP directed GDP and ADP reduction, respectively. Pool measurements of NDPs, NTPs, and dNTPs in the cultivated bloodstream form of trypanosomes exposed to deoxyribonucleosides or inhibited by hydroxyurea confirmed our in vitro allosteric regulation model of ribonucleotide reductase. Interestingly, the trypanosomes had extremely low CDP and CTP pools, whereas the dCTP pool was comparable with that of other dNTPs. The trypanosome ribonucleotide reductase seems adapted to this situation by having a high affinity for the CDP/UDP-specific effector dATP and a high catalytic efficiency, K cat /K m , for CDP reduction. Thymidine and deoxyadenosine were readily taken up and phosphorylated to dTTP and dATP, respectively, the latter in a nonsaturating manner. This uncontrolled uptake of deoxyadenosine strongly inhibited trypanosome proliferation, a valuable observation in the search for new trypanocidal nucleoside analogues.Trypanosoma brucei is an African unicellular eukaryote that lives extracellularly in the mammalian bloodstream and central nervous system as well as in the guts and salivary glands of tsetse flies. Residing in its mammalian host, it causes a fatal disease called sleeping sickness. There is an urgent need to find new chemotherapy against this disease because the current ones are limited by toxicity as well as an increasing resistance among the trypanosomes (1).Ribonucleotide reductase (2) is a key enzyme in DNA synthesis because it catalyzes the reduction of ribonucleotides to deoxyribonucleotides, a reaction assisted by a protein-bound or a 5Ј-deoxyadenosyl cobalamin-derived free radical. Primarily based on the nature of this radical, the ribonucleotide reductases are divided into three classes where most of the eukaryotic and some of the prokaryotic ones belong to class I. The enzymes in this class are heterodimers formed from two large (R1) and two small (R2) polypeptides. The R1 protein binds substrates and allosteric effectors, whereas the R2 protein contains a tyrosyl radical essential for enzyme activity. The radical can be scavenged by the one-electron reductant hydroxyurea, a drug that has been in clinical use against leukemias (3).Except those from the Herpesviridae family (4), all ribonucleotide reductases studied are allosterically regulated. The nonviral class I enzymes have two types of allosteric effector binding sites called the activity site (lacking in certain bacterial ribonucleotide reductases specifically called class Ib) and the specificity site (2). The activity site determines...

The effect of black seed oil (Nigella sativa oil) on parasitaemia, some serum and liver enzymes as well as some haematological parameters in Trypanosoma brucei-infected rats was investigated. The results show there was low parasitaemia and extension of life span of rats from 12 days of the infected untreated (control) rats to 22 days for the infected black seed oil-treated rats. Results also show significant increases in activities of serum alkaline phosphatase as well as glutamate oxaloacetate and glutamate pyruvate transaminases with decreases in the liver enzyme activities. Protein concentrations show significant decreases in the serum and increases in the liver. There were also significant increases in the haemoglobin (Hb) concentration, packed cell volume (PCV), red blood cell (RBC), white blood cell (WBC) and platelet counts of infected oil-treated rats when compared with the infected untreated. We suggest that black seed oil has trypanocidal properties and probably stimulate the host immune system to control parasite proliferation thereby making it a possible agent for managing African sleeping sickness despite possible gradual damage to host organs as shown by increases in some serum enzymes.

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Alkaline phosphatase, glutamate oxaloacetate transaminase and glutamate pyruvate transaminase activities were assessed in rats highly infected with federe strain of Trypanosoma brucei and treated with honey. Therapeutic effect of honey on parasitaemia was also assessed. Results show an extension in the life span of infected but treated rats from 12 days for control to 19 days for infected honey-treated rats. Parasitaemia was also effectively lowered. Alkaline phosphatase activity was increased in the serum but not significantly different in the liver. Glutamate oxaloacetate transaminase and glutamate pyruvate transaminase were also increased in the serum but there is decrease in glutamate pyruvate transaminase activity in the liver. There were no significant differences in glutamate oxaloacetate transaminase activity in the liver. Results suggest that, honey could be a potential agent in the management of African trypanosomosis. However, it leads to decrease in glutamate pyruvate transaminase activity in the liver suggesting liver damage. Increase in glutamate oxaloacetate transaminase and alkaline phosphatase activities in the serum also suggest possible damage to other organs where these maybe abundant.