Hydrogenosomes in a mixed isolate of Isotricha prostoma and Isotricha intestinalis from ovine rumen contents

1. Both Isotricha intestinalis and I. prostoma possess microbody-like organelles, with a highly granular appearance. 2. These organelles, which are sedimentable at 10(5) g-min, bear no morphological similarity to mitochondria, but are enzymatically similar to organelles possessed by certain other anaerobic protozoa and termed hydrogenosomes. 3. The hydrogenosomes isolated from a preparation of mixed isotrichs bear a closer similarity to those isolated from the other rumen holotrich. Dasytricha ruminantium, than those recently identified in a mixed entodiniomorph preparation, or the trichomonads, in that the enzyme malate dehydrogenase (decarboxylating) is non-sedimentable and phosphoacetyl transferase together with acetate kinase are involved in the transformation of acetyl CoA to acetate. 4. The results enable a scheme of acetate, CO2 and H2 formation from carbohydrates to be proposed and extends the number of protozoa known to possess this organelle.     

Plagiarism of the host immune system: lessons about chemokine immunology from viruses

In their attempts to evade the host immune response, mammalian viruses have evolved a wide range of strategies. These include the expression and modification of various host cytokines and receptors. Understanding the mechanism of action of these virally encoded proteins will clearly deepen our insights into immunology. In the past few months several new virally encoded chemokines have been described which can modify both the host immune and antiviral response. Their manipulation of the cytokine structure-function relationship may also be useful in the development of reagents for treating immune and proliferative diseases.     

Protein methylases in Trypanosoma brucei brucei: activities and response to DL-alpha-difluoromethylornithine

Protein methylases I, II and III were detected in extracts of Trypanosoma brucei brucei, and characterized according to the specific amino substituent methylated. Only protein methylase II activity was elevated by difluoromethylornithine treatment of T. b. brucei, and hence this enzyme was characterized further. Protein methylase II transferred methyl groups from S-adenosyl-L-methionine (S-AdoMet) to the carboxyl residues of several protein substrates, exhibiting highest activity with histone VIII-S (arginine-rich subgroup f3). The crude enzyme had an apparent Km for histone VIII-S of 28 mg ml-1 (11.4 mM-aspartyl and 18.4 mM-glutamyl residues methylated), and an apparent Km for S-AdoMet of 8.4 microM. T. b. brucei protein methylase II was sensitive to inhibition by S-adenosyl-L-homocysteine and its analogue sinefungin with apparent Ki values of 12.9 and 1.6 microM, respectively. Using a partially purified preparation, analysis of kinetic data in the presence and absence of sinefungin indicated that this analogue acts as a competitive inhibitor of the S-AdoMet binding site, and as a non-competitive inhibitor of the (protein) histone VIII-S binding site. The possible role of the enzyme in morphological control and its potential as a chemotherapeutic target are discussed.