Inter-relationships of Serine, Glycine and Vitamin B6 in the Growth of Mutants of Escherichia coli

Abstract

SUMMARY: Five mutants of Escherichia coli which grow to a greater or less extent when the minimal medium is supplemented with vitamin B, have been studied. They fall into two groups according to the further effect of serine + glycine on growth.(1) Two strains showed full and rapid growth with pyridoxine alone and serine + glycine neither replaced this vitamin nor enhanced growth in its presence. (2) Three strains showed delayed and suboptimal growth with pyridoxine alone. With these serine + glycine had two effects: (a) it decreased the lag and enhanced the final extent of growth when added with pyridoxine ; (b) it permitted suboptimal growth in the absence of pyridoxine. The second effect was dependent on (two strains), or greatly increased by (one strain), the concurrent addition of glycolaldehyde.Nothing is known of the pathway of synthesis of vitamin B, by organisms not requiring an external source of it for growth. Mutant strains of Escherichia coli which multiply only when vitamin B, is supplied are more rare than those which respond to vitamin B, or serine or glycine. The simplest explanations of the apparent replacement of the vitamin by these amino acids are: ( a ) the amino acids are end products of reactions catalysed by vitamin B, derivatives; consequently, when provided preformed, they decrease or abolish the need for the vitamin; ( b ) the synthesis of serine and glycine by the organism is limited, and one or other is a reactant a t some step in the biosynthesis of vitamin B,.A detailed study was made of the properties of mutants of this type in an attempt to discover an immediate biochemical lesion resulting from the mutation and possibly to obtain some conception of the route of synthesis of vitamin B, and its derivatives by normal strains of Escherichia coli. METHODSEscherichia coli. Stock cultures were maintained on tryptic meat agar slopes and were subcultured monthly (16 hr. a t 37" , 1955) which required vitamin B, for growth a t 37" but responded also to certain mixtures of amino acids at lower temperatures.Strain B166 was used for most of the work to be described.

The Catabolism of Cystathionine by Escherichia coli

“…The present work shows that E. coli has active enzymic mechanisms for the conversion of cystathionine to homocysteine which is the undoubted immediate precursor of methionine. Other work in this laboratory (Rowbury, 1961(Rowbury, , 1962 shows that E. coli also has enzymes for the synthesis of cystathionine from precursors (homoserine + cysteine) indicated by nutritional studies with mutants of E , coli and other micro-organisms. There remains little doubt therefore that cystathionine is an intermediate and that the results of the isotope experiments must be explained in some other way; it is possible, for example, that exogenous cystathionine may not equilibrate with the cystathionine formed within the organism and perhaps remains tightly bound to the enzyme systems which catalyse its synthesis and further metabolism.…”

“…Media and growth. Medium L (Morris & Woods, 1959), containing lactate as carbon source, was used for strain F. Medium A, used for the auxotrophic strains, was the glucose + salts medium of Davis & Mingioli (1950) except that the glucose (and any necessary growth factor) was added before autoclaving. With strain B 166 it was desired to obtain organisms grown without added pyridoxin; although either DL-serine or glycine alone will support growth under these conditions, best yields were obtained with a mixture of DL-serine, glycine and DL-alanine (each mM).…”

The Synthesis of Vitamin B6 by some Mutant Strains of Escherichia coli

“…'Activated glucose' refers to solutions of glucose in O-O4~-phosphate buffer (pH 7.4) autoclaved at 115' for 7 min. All other chemicals were as described by Morris & Woods (1959).…”

Biosynthesis of Vitamin B6

“…By testing the growth effects of varying in gredients of the media on which a series of vitamin B6-requiring mutants of E. coli were grown, Woods and Morris came to the con clusion that seriee, glycine and glycolaldehyde are possible precursors in the biosynthesis of vitamin B6 in E, coli. However, no isotopic experiments have yet been performed to con firm the hypothesis that any or all of these compounds are true precursors of vitamin B6 (5,6). Recently, Lunan and West isolated the 14C -labeled pyridoxamine from Candida utilis , Serine-3-14C, acetate-l-14C, alanine-1-14C and acetate-2-14C gave rise to 14C-labeled pyridoxa mine.…”