Regulation of amino acid transport in growing cells of Streptomyces hydrogenans. I. Modulation of transport capacity and amino acid pool composition during the growth cycle

Preparation and purification of the proteinase inhibitor, leupeptin, from culture filtrates of Streptomyces lavendulae

Leupeptin (N-acetyl-L-leucyl-L-leucyl-L-argininal) was produced as an extracellular metabolite by Streptomyces lavendulae. Addition of lysine to the growth medium stimulated leupeptin production from 200 to 1400 micrograms/ml. Incubation of late exponential phase mycelium in a synthetic medium was used to prepare single labelled (3H) and double labelled (3H/14C) inhibitor for metabolic studies. An improved purification scheme that generates leupeptin of high purity with good recoveries is also reported.

Regulatory mutants of Streptomyces clavuligerus affected in free diaminopimelic acid content and antibiotic biosynthesis

The composition of intracellular free amino acid pools was determined in Streptomyces clavuligerus mutants possessing an altered aspartokinase which is insensitive to concerted feedback inhibition by threonine and lysine. These mutants contained total free amino acid pool contents that were considerably higher than those found in the wild-type strain. Diaminopimelic acid accounted for 10 to 20% of the total free amino acid pools, depending on the individual mutant and its culture growth phase, whereas diaminopimelic acid contained in the wild-type strain accounted for only 0.5% of the total free amino acid pool.

Amino-acid transport in suspension-cultured plant cells : V. Influence of L-leucine, carbon-free and nitrogen-free media on L-leucine uptake

The carrier system which transports L-leucine (L-leu) into suspension-culturedNicotiana tabacum L. cv. Wisconsin 38 cells appeared to be constitutive since it was always present and was not induced by L-leu even in nitrogen-starved cells. However, L-leu uptake rates for cells grown in medium containing L-leu were transiently reduced as a result of either transinhibition or repression. Growth-phase cells appeared to have more L-leu carriers per unit area of membrane than stationary-phase cells, and for this reason growing-phase cells exhibit higher L-leu uptake rates. These higher rates reflect a physiological or developmental condition since growth-phase cells did not dramatically change their L-leu uptake rates when subcultured, while stationary-phase cells doubled their rates within 6 h after being subcultured. Cells grown in a medium lacking a useable carbon souce had uptake rates higher than control rates for several days. These higher rates peaked after about 1 d and then decreased over the next several days. Cells grown in a medium lacking a nitrogen souce responded similarly except that the increased rates peaked after about 3 d and persisted longer. Kinetic analysis of uptake rates in cells grown without a carbon souce for 1 d or without a nitrogen souce for 3 d indicated that the L-leu carrier had Kms similar to those of untreated cells. These results indicate that cultured tobacco cells respond to their environment by increasing or decreasing the number or activity of kinetically similar L-leu carriers.

Turnover of proteins in asporogenic Bacillus megaterium. Evidence for a gradual decrease of the turnover rate

The rate of protein turnover in asporogenic Bacillus megaterium decreases continuously during incubation in a sporulation medium. The capability of equilibration of external amino acids with amino acids in the metabolic pool of non-growing cells was retained for at least 5 h. Leucine, while repressing the synthesis of the exocellular protease, does not significantly influence the course of protein degradation in vivo. Transfer of non-growing cells after 4 h to a fresh sporulation medium does not influence the rate of protein degradation. The gradual decrease of the rate of protein turnover in non-growing cells of the asporogenic variant is thus not an artifact caused by a decreased uptake of amino acids by cells or by conditions under which the protein turnover is determined.

Regulative influence of o-aminobenzoic acid (OABA) on the biosynthesis of nourseothricin in cultures of Streptomyces noursei JA 3890b. V. Effect of OABA on cytochrome levels and amino acid transport

o-Aminobenzoic acid (OABA) known by its stimulatory effect on streptothricin biosynthesis by Streptomyces noursei JA 3890b was found to suppress specifically the formation of cytochrome a-type terminal oxidase while the levels of the b- and c-type cytochromes apparently remained unaffected. This change was coupled to decreased capacity of transport of u-14C-L-alanine and u-14C-L-glutamic acid into the mycelium, giving rise to delay of amino acid catabolism and decreased production of nitrogen catabolites within the cell. The above results provide supporting evidence for conjectures recently published by us concerning the control by nitrogen catabolites of the secondary metabolism of this strain. As a summary a scheme is proposed showing several hypothetic mechanisms by which nitrogen catabolite regulation of nourseothricin production could be accomplished.

Regulation of macromolecular synthesis during hyphal germ tube emergence from Mucor racemosus sporangiospores

Protein and RNA syntheses were examined during hyphal germ tube emergence from sporangiospores of a dimorphic phycomycete, Mucor racemosus. Both classes of macromolecules were synthesized immediately upon introduction of the dormant sporangiospores into nutrient medium. The specific rates of synthesis of both protein and RNA accelerated during initial germ tube emergence and reached a maximum when the emergence of new germ tubes ended. The specific rates of synthesis later decreased during further hyphal elongation. The distribution of ribosomes between active polysomes and monosomes and inactive subunits was determined by sucrose density gradient centrifugation, and the rate of amino acid addition to nascent polypeptide chains was calculated throughout the developmental sequence. The results showed that both the percentage of ribosomes active in protein synthesis and the velocity of ribosome movement along the mRNA were continuously adjusted throughout hyphal germ tube development. The free intracellular amino acid pools were measured throughout development. Alanine, glutamate, and aspartate were present at very high concentrations in the dormant spores but were rapidly depleted during hyphal germ tube emergence. The results of these studies are discussed in relation to hyphal germ tube development from yeast cells of Mucor and dormant spores of other fungal species.

Effect of dibutyryl cyclic adenosine monophosphate on active amino acid transport in Streptomyces hydrogenans

The active uptake of 2-aminoisobutyric acid (AIB) and several other amino acids in resting cells of Streptomyces hydrogenans was found to be stimulated by exogenously added adenosine cyclic monophosphate (cAMP). The uptake of glycerol, sorbose, and pyrimidine nucleosides remained unaffected. Among the various cAMP derivatives tested, the dibutyryl derivative was found to be most effective, followed by monobutyryl cAMP, and cAMP. Dibutyryl cGMP was also found to stimulate AIB transport, and its effectivity was as good as that of dibutyryl cAMP. The effect of dibutyryl cAMP is time dependent and attains its maximum after 40--60 min of incubation at 30 degrees C in K-Na-phosphate buffer. Dibutyryl cAMP-dependent transport stimulation has a high temperature coefficient and is prevented by rifamycin SV or chloramphenicol. The rate of leucine incorporation into protein was rapidly increased upon addition of dibutyryl cAMP. Kinetic studies reveal that the stimulation of AIB transport is characterized by an increase in maximum uptake rate and an unaltered apparent Michaelis constant. Analysis of the unidirectional fluxes show that both influx and efflux are enhanced by dibutyryl cAMP. It is concluded that exogenous dibutyryl cAMP stimulates de novo synthesis of certain proteins including the transport catalysts for various amino acids.

Amino acid transport and metabolism in nitrogen-starved cells of Saccharomyces cerevisiae

Nitrogen-starved yeast derepress a general amino acid permease which transports basic and hydrophobic amino acids. Although both groups of amino acids are metabolized, the derivatives of the basic amino acids are retained by the cells, whereas those of the hydrophobic amino acids are released as acidic and neutral deaminated derivatives. The release of the deaminated derivatives of the hydrophobic amino acids only occurs in the presence of glucose, which presumably produces amino acceptors. The accumulation of intracellular amino acids results in trans-inhibition of the uptake of exogenous amino acids whether the intracellular amino acid is a basic amino acid or the product of intracellular transamination from a hydrophobic amino acid. Variation of permease and transaminase activity was measured during growth under repressed (ammonia-grown) and derepressed (proline-grown) conditions. Maximum levels for both activities occurs at the mid-exponential phase.

Regulation of amino acid transport in growing cells of Streptomyces hydrogenans. II. Correlation between transport capacity and growth rate in chemostat cultures

The uptake of various amino acids into Streptomyces hydrogenans grown in chemostatically and turbidostatically controlled steady state cultures has been investigated. A close correlation between transport capacity and the growth rates of the cells was found. As shown by kinetic analysis, the increased transport is due to elevated maximum uptake rates, the apparent Michaelis constants remaining unchanged. Analysis of the unidirectional fluxes of cycloleucine revealed that not only the influx is raised as the growth rate is increased but also the efflux. Hence, the conclusion is drawn that the growth-rate dependent modulation of transport capacity is, at least, partially due to the variation of the concentration of active transport components. Since the cells were grown in the absence of external amino acids the results suggest that amino acid transport into S. hydrogenans is under control of endogenous effectors.