Arnold L. Demain

Reversal of lysine inhibition of penicillin production by α-aminoadipic or adipic acid

Abstract l -Lysine inhibition of penicillin synthesis by resting cells of Penicillium chrysogenum in a synthetic medium was confirmed. Stimulation of the rate of antibiotic formation by α-aminoadipic acid was observed in the same system. In a complex medium allowing growth of the fungus, lysine inhibition was reversed by α-amino-adipic acid or, to a lesser degree, by adipic acid. The relative concentrations of lysine and α-aminoadipic acid appear to be extremely important in the penicillin fermentation. The data suggest, that α-aminoadipic acid has a role in penicillin biosynthesis; lysine apparently interferes with this role.

Inhibition of penicillin formation by amino acid analogs

Abstract Using resting mycelial suspensions, it was found that S -ethyl- dl -cysteine and α-methyl- dl -valine inhibit penicillin synthesis from lactose. Reversal by l -cystine and l -valine, respectively, was observed. Whereas l -valine can be used for penicillin synthesis, the d -form is an inhibitor. Conclusions based on previous tracer studies were confirmed.

Industrial fermentations and their relation to regulatory mechanisms.

Publisher Summary This chapter discusses the industrial fermentations and their relation to regulatory mechanisms. The success of an industrial fermentation does not depend on addition of precursors. Rather, the effects of regulatory mechanisms such as feedback inhibition and repression are of extreme importance. Modification of feedback effects without destroying the metabolic activities of the cell has become a major activity of the fermentation microbiologist. Such alteration in living cells can be done by decreasing the concentration of the end product, and modifying the sensitive enzyme or enzyme-forming system. Regulatory controls probably affect antibiotic production as well. The inhibition of penicillin formation by lysine and the stimulation of biosynthesis of cephalosporin C by methionine are apparently the results of normal feedback effects of these amino acids on their own biosynthesis. Knowledge of control mechanisms can be expected to stimulate effort towards the industrial production of microbial enzymes and nucleic acids. Constitutive mutants have already been obtained, producing 25% of their protein as a single enzyme. The chapter also briefly discusses the synthesis of macromolecules.

The mechanism of penicillin biosynthesis.

Publisher Summary This chapter discusses the mechanism of penicillin biosynthesis. Penicillin is produced by strains of Penicillium notatum or Penicillium chrysogenum when inoculated into a suitable nutrient medium. The biosynthesis of benzyl penicillin occurs via the condensation of its precursors, phenyl acetic acid, L-cysteine, and L-valine. The rate-limiting reaction is the synthesis of the side-chain precursor, and thus phenyl acetate is usually added to the fermentation medium. Acylation of the β-lactam-thiazolidine ring appears to be one of the final steps in biosynthesis. A large number of compounds are capable of being incorporated into the cysteine moiety of penicillin. Added L-cystine (after conversion to L-cysteine) is used as an intact molecule for penicillin synthesis. The incorporation is stereo specific for the L-form, which is the configuration present in penicillin. The remaining portion of the molecule is synthesized from t-valine despite the fact that the valine moiety of penicillin is of D-configuration. Results of several studies have indicated that the intact carbon skeleton of valine is used, but the amino group is lost during biosynthesis.

Antagonism by purines and derivatives in the nutrition of a Bacillus subtilis mutant

Abstract A guanineless mutant of Bacillus subtilis was subject to inhibition by normal purines and derivatives. The wild-type was not inhibited. Utilization of guanine was inhibited by adenine and hypoxanthine. Guanosine utilization was mainly antagonized by adenosine and inosine. Growth on guanosine-5′-phosphate was even more strongly inhibited by adenosine and inosine. Inosine-5′-phosphate and adenosine-5′-phosphate were weaker inhibitors of guanosine-5′-phosphate utilization than were the nucleosides. Xanthine and xanthosine failed to inhibit. The simplest interpretation of the results implicates the permeation of guanine as the site of adenine and hypoxanthine inhibition and the penetration of guanosine as the site of adenosine and inosine inhibition. Guanosine-5′-phosphate is thought to undergo a prior extracellular hydrolysis to guanosine before utilization.

Catabolism of betaine and its relationship to cobalamin overproduction

Abstract Incorporation of radioactivity from [ Me 14 C]betaine into cobalamin by Pseudomonas denitrificans is indirect and apparently is unrelated to the betaine (or choline) requirement for overproduction for cobalamin. An incorporation scheme involving catabolism of betaine to glycine, one carbon units, and succinyl-CoA is proposed to explain the incorporation data. In accordance with this scheme, [ Me - 14 C]betaine and [2- 14 C]betaine are incorporated into cobalamin but not [1- 14 C]betaine. Methionine dilutes out the incorporation of radioactivity from [ Me - 14 C]betaine and appears to be the precursor of the “extra” methyl groups of cobalamin, i.e. , those methyl groups not derived from porphobilinogen. The true role of betaine or choline in cobalamin over-production is thought to be of a regulatory nature and to apply to general porphyrin synthesis as well.