Testosterone 5 alpha-reductase in rat brain

We describe a simple procedure for the microassay of testosterone 5 alpha-reductase in homogenates of rat brain. This enzyme converts testosterone to dihydrotestosterone. We have used this assay to characterize the enzymatic activity and to map its distribution. The apparent Km is 4.1 x 10(-6) M and the Vmax is 85.6 pmol/mg protein/h. The pH optimum is broad and extends from pH 6.0 to 8.0. For the brain regions surveyed, testosterone 5 alpha-reductase activity varied over a 10-fold range. The highest activities were observed in homogenates of the midbrain and pons (37-39 pmol/mg protein/h). The lowest were seen in homogenates of the thalamus, caudate nucleus, frontal cortex, hippocampus, hypothalamus, olfactory tubercle, and preoptic area (3-7 pmol/mg protein/h).     

Recognition of Leishmania donovani antigens by murine T lymphocyte lines and clones. Species cross-reactivity, functional correlates of cell-mediated immunity, and antigen characterization

Studies in man and experimental animals suggest that cell-mediated immunity is of primary importance in limiting the pathogenesis of cutaneous and visceral leishmaniasis. In an attempt to determine, more directly, the role of T lymphocytes and the nature of the antigens that activate them, we have propagated antigen-specific murine T lymphocyte lines and clones that proliferate in response to antigens present on the membrane of intact Leishmania donovani promastigotes. One such line cross-reacts with membrane antigens on seven other Leishmania species and, to a lesser extent, with antigens on African procyclic trypanosomes. T lymphocyte clones that also exhibited a broad range of species cross-reactivity were isolated. About 40% of these clones had highly restricted specificity, whereas 60% were more extensively cross-reactive. The parent line and some clones passively transferred footpad DTH when injected locally, and some secreted a lymphokine activity that elicited intracellular killing of amastigotes within infected macrophages. Although the proliferative response of most clones was H-2 restricted, two clones appeared to be reactive in the presence of allogeneic antigen presenting cells. The majority of the clones appeared to recognize carbohydrate containing antigens, and absorption with solid substrate-bound lectins indicated that these antigens contained both mannose and galactose ligands. The antigenic activity was also absorbed using either of two extensively cross-reactive anti-parasite monoclonal antibodies.     

Biosynthesis of polyketides. Purification and inhibition studies of 6-methylsalicylic acid synthase

6-MSA³ synthase has been purified 190-fold with 33% yield. The purification was found to be dependent on the presence of glycerol. The acetylenic inhibitors 3-pentynoyl- and 2-hexynoyl-NAC completely inhibit 6-MSA production at concentrations in which fatty acid synthesis, TAL production as well as NADPH oxidation are only partially affected. These results confirm earlier studies on the specificity of inhibition by acetylenic inhibitors and support a mechanism wherein the NADPH-mediated reduction step occurs on a 6-carbon rather than on an 8-carbon intermediate.