1. A method is described by which good yields of ribosomes and polysomes free of contamination by submitochondrial fragments can be prepared from rat cardiac muscle. These preparations are capable of incorporation of amino acids into protein in vitro. 2. The ribosome preparation consists of 32% of monomeric ribosomes and 68% of ribosomal aggregates or polysomes. The polysome preparation has a decreased monomeric content. Dimers, trimers, tetramers, pentamers and larger components can be differentiated. 3. The polysome aggregate structure is degraded to monomeric ribosomes on incubation with small amounts of ribonuclease or by preparation in the absence of Mg(2+) ions. The degradation in the absence of Mg(2+) ions was not reversible and drastically decreased the incorporation of amino acids in vitro. 4. The cardiac ribosomes contained two major RNA species sedimenting at 19s and 28s in a 1:2.4 ratio. 5. The RNA/protein ratio of cardiac ribosomes and polysomes was consistently lower than that of similar preparations from liver. The concentrations of Na(+) and K(+) ions present during preparation had a great effect on the RNA/protein ratio. 6. Optimum conditions for the incorporation of amino acids into protein in vitro are reported. Cardiac ribosomes have a lower rate of incorporation of amino acids in vitro than liver ribosomes. 7. Heart cell sap is less active than liver cell sap: evidence is presented that a factor, present in liver cell sap and concerned with stimulating the synthesis of the peptide chain, is lacking in heart cell sap. 8. Pulse-labelling of perfused hearts followed by examination of the subcellular structures showed that the ribosomal fraction was the most active in the incorporation of amino acids in vitro.

Discovering bioactive metabolites within a metabolome is challenging because there is generally little foreknowledge of metabolite molecular and cell-targeting activities. Here, single-cell response profiles and primary human tissue comprise a response platform used to discover novel microbial metabolites with cell-type-selective effector properties in untargeted metabolomic inventories. Metabolites display diverse effector mechanisms, including targeting protein synthesis, cell cycle status, DNA damage repair, necrosis, apoptosis, or phosphoprotein signaling. Arrayed metabolites are tested against acute myeloid leukemia patient bone marrow and molecules that specifically targeted blast cells or nonleukemic immune cell subsets within the same tissue biopsy are revealed. Cell-targeting polyketides are identified in extracts from biosynthetically prolific bacteria, including a previously unreported leukemia blast-targeting anthracycline and a polyene macrolactam that alternates between targeting blasts or nonmalignant cells by way of light-triggered photochemical isomerization. High-resolution cell profiling with mass cytometry confirms response mechanisms and is used to validate initial observations.

Apoptolidin A has been described as among the top 0.1% most cell selective cytotoxic agents to be evaluated in the NCI 60 cell line panel. The molecular structure of apoptolidin A consists of a 20-membered macrolide with mono- and disaccharide moieties located at C9 and C27, respectively. In contrast to apoptolidin A, the aglycone (apoptolidinone) shows no cytotoxicity (>10 μM) when evaluated against several tumor cell lines. Apoptolidin H, the C27 deglycosylated analog of apoptolidin A, was produced by targeted glycosyl transferase gene deletion and displayed sub-micromolar activity against H292 lung carcinoma cells. Selective esterification of the C2′ hydroxyl group of apoptolidins A and H with 5-azidopentanoic acid afforded azido functionalized derivatives of potency equal to their parent macrolide. Azido apoptolidins readily underwent strain-promoted alkyne azido cycloaddition (SPAAC) reactions to provide access to fluorescent and biotin functionalized probes. Microscopy studies demonstrate apoptolidins A and H localize in the mitochondria of H292 human lung carcinoma cells.

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Apoptolidin A has been described as among the top 0.1% most cell selective cytotoxic agents to be evaluated in the NCI 60 cell line panel. The molecular structure of apoptolidin A consists of a 20-membered macrolide with mono-and disaccharide moieties located at C9 and C27, respectively. In contrast to apoptolidin A, the aglycone (apoptolidinone) shows no cytotoxicity (>10 μM) when evaluated against several tumor cell lines. Apoptolidin H, the C27 deglycosylated analog of apoptolidin A, was produced by targeted glycosyl transferase gene deletion and displayed sub-micromolar activity against H292 lung carcinoma cells. Selective esterification of the C2′ hydroxyl group of apoptolidins A and H with 5-azidopentanoic acid afforded azido functionalized derivatives of potency equal to their parent macrolide. Azido apoptolidins readily underwent strain-promoted alkyne azido cycloaddition (SPAAC) reactions to provide access to fluorescent and biotin functionalized probes. Microscopy studies demonstrate apoptolidins A and H localize in the mitochondria of H292 human lung carcinoma cells.Keywords natural products; antitumor; polyketides; metabolism; chemical probeThe apoptolidins are macrocylic natural products produced by an actinomycete (Nocardiopsis sp. FU40) soil microbe by way of a type I polyketide synthase biosynthetic pathway. [1] Apoptolidin A (1) was reported to induce cell death in E1A transformed rat glia cells, a model cancer cell phenotype, while not affecting the growth of non-transformed glia cells. [2] The described selective cytotoxicity of apoptolidin A stimulated interest in its total synthesis and mechanism of induced cell death. [3] Salomon and Khosla employed a pharmacological approach to define the mechanism of cell death using LYas mouse lymphoma cells and concluded cell death proceeded by way of the mitochondria mediated apoptotic pathway (intrinsic pathway). Following the reported isolation of apoptolidin A (1), other structural variants have been described either as minor microbial metabolites, [5] products of isomerization [6] or semi- [7] and total synthesis [8] . When evaluated for cytotoxicity against tumor cells, these apoptolidins reveal considerable tolerance of structural modifications within the macrolide core including deoxygenation [apoptolidins B and C] In contrast to structural changes within the core macrolides, removal of the deoxy sugars resulted in complete loss of activity with EC 50 values of apoptolidinone A (4) and C (5) reported to be greater then 10 μmol against several tumor cell lines in cell viability assays. [8c,9] The observed loss in activity upon exhausitive deglycosylation of the core macrolide presented an opportunity to develop a series of apoptolidin derived probes to support mechanism of action studies. We report here methods to access apoptolidins of varying state of glycosylation (tri-, di-, mono and non-glycosylated) and preliminary studies on their use as cellular probes.Apoptolidin A (1) is readily obtained by fermentation of the actinomyce...

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1. At 3 min after an intravenous injection of radioactive amino acids into the rat, the bulk of radioactivity associated with liver polyribosomes can be interpreted as growing peptides. 2. In an attempt to identify the rate-limiting step of protein synthesis in vivo and in vitro, use was made of the action of puromycin at 0 degrees C, in releasing growing peptides only from the donor site, to study the distribution of growing peptides between the donor and acceptor sites. 3. Evidence is presented that all growing peptides in a population of liver polyribosomes labelled in vivo are similarly distributed between the donor and acceptor sites, and that the proportion released by puromycin is not an artifact of methodology. 4. The proportion released by puromycin is about 50% for both liver and muscle polyribosomes labelled in vivo, suggesting that neither the availability nor binding of aminoacyl-tRNA nor peptide bond synthesis nor translocation can limit the rate of protein synthesis in vivo. Attempts to alter this by starvation, hypophysectomy, growth hormone, alloxan, insulin and partial hepatectomy were unsuccessful. 5. Growing peptides on liver polyribosomes labelled in a cell-free system in vitro or by incubating hemidiaphragms in vitro were largely in the donor site, suggesting that either the availability or binding of aminoacyl-tRNA, or peptide bond synthesis, must be rate limiting in vitro and that the rate-limiting step differs from that in vivo. 6. Neither in vivo nor in the hemidiaphragm system in vitro was a correlation found between the proportion of growing peptides in the donor site and changes in the rate of incorporation of radioactivity into protein. This could indicate that the intracellular concentration of amino acids or aminoacyl-tRNA limits the rate of protein synthesis and that the increased incorporation results from a rise to a higher but still suboptimum concentration.

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