Cellular uptake of L-lactate in mouse diaphragm.

Early uptake curves of L-lactate and of mannitol were measured in quartered, incubated mouse diaphragms. Uptake was determined at 15, 30, and 45 s for various concentrations of lactate in the external solution as well as in the presence and absence of the competitive inhibitor of lactate transport, alpha-cyano-4-hydroxycinnimate. In normal preparations, when the external lactate concentration was 10 mM or less, the ratio of lactate-to mannitol space in the tissue was 1.7. This value was nearly independent of time and of external concentration. In normal preparations, when the external lactate concentration was greater than 10 mM, the ratio of lactate-to-mannitol space rose with time. At a fixed time, however, this ratio fell with increasing lactate concentration. In the inhibited preparations, the ratio of lactate-to-mannitol space rose with time at all concentrations. When lactate concentration was greater than 5 mM, this ratio was independent of the external concentration. The results suggest that there are two modes of lactate entry into these muscle cells. Entry can occur by means of a saturable system. When external lactate concentration is low, entry rates for this process are rapid compared with diffusional rates. This system probably saturates at concentrations near 10 mM and can facilitate transport in either direction. In addition, an appreciable passive leak is present. This leak accounts for about one fourth of the membrane transfer when external lactate is low, but is equal to the carrier transfer when lactate concentration is 30 mM. A model was developed to describe the entry of a permeating solute, such as lactate, into an isolated tissue.     

The inefficiency of ribosomes functioning in Escherichia coli growing at moderate rates

It is generally agreed that ribosomes function with reduced efficiency (i.e. a smaller proportion is actually engaged in protein synthesis) in bacteria growing at low growth rates (doubling times greater than 2 h). This paper examines whether the efficiency is constant in bacteria growing at various rates corresponding to doubling times of less than 2 h. Because isotopic methods cannot be used in very rich media, turbidimetric methods have been extended to follow the kinetics of growth immediately following the shift-up of cultures of Escherichia coli ML308 growing in glucose minimal medium or succinate minimal medium into a very rich medium supporting a balanced doubling time of 17.4 min. It is concluded that the efficiency of ribosome participation in protein synthesis is higher in the very rich medium than in the two minimal media, which support doubling times of 43 and 65 min, respectively, at 37 degrees C.     

Acyldiglucosyldiacylglycerol-containing lipoteichoic acid with a poly(3-O-galabiosyl-2-O-galactosyl-sn-glycero-1-phosphate) chain from Streptococcus lactis Kiel 42172.

The lipoteichoic acid of Streptococcus lactis Kiel 42172 was isolated. The lipid portions were released by HF and were established to be 3-O-[O-alpha-D-galactopyranosyl-(1 leads to 6)-alpha-D-galactopyranosyl]-2-O-alpha-D-galactopyranosyl-sn-glycero-1-phosphate, they are joined by phosphodiester bonds nosyl)]glycerol. The repeating units of the hydrophilic chain were established to be 3-O-[O-alpha-D-galactopyranosyl-(1 leads to 6)-alpha-D-galactopyranosyl]-2-O-alpha-D-galactopyranosyl-sn-glycero-1-phosphate; they are joined by phosphodiester bonds at carbon atom 6 of the galabiosyl residues. The innermost unit is linked to the glycolipid by a phosphodiester presumably at C-6 of the outer glucosyl moiety. The hydrophilic chain is 7.4--11.8 units in length, measuring 12--19 nm is extended conformation. The content of 2.7--2.96 acyl groups per 2 glucosyl residues indicates that 70--96% of the glycolipid consists of acyldiglucosyldiacylglycerol. The novel poly(glycosylgly-cerophosphate) structure provided for the first time the oplipoteichoic acids are the sn-1 isomer which has previously been suggested from biosynthetic studies (Glaser, L., & Lindsay, B. (1974) Biochem. Biophys. Res. Commun. 59, 1131--1136).     

Mutator mutations in bacteriophage T4 gene 32 (DNA unwinding protein).

Bacteriophage T4 gene 32 encodes a DNA unwinding protein required for DNA replication, repair, and recombination. Gene 32 temperature-sensitive mutations enhance virtually all base pair substitution mutation rates.     

ISolation and identification of a sulfur-containing metabolite of spironolactone from human urine

In the urine of normal subjects Who were given an oral dose of 500 mg spironolactone (3-(3-oxo-7α-acetylthio-17β-hydroxy-4-androsten-17α-yl)-propionic acid γ-lactone; Aldactone^R) together with 100, uCi H-20, 21 spironolactone, a so far unknown major metabolite has been detected by thin layer chromatography. The metabolite then could be isolated by means of counter-current-distribution. According to masspectral and magnetic resonance data, the metabolite has been assigned the structure of 3-(3-oxo-7α-niethyl sulfonyl-6β, 17β-dihydroxy-4-androsten-17α-yl)-propionic acid γ-lactone. By oxidation of the corresponding methylsulfinyl compound — another already known metabolite of spironolactone-with m-chloroperbenzoic acid, a compound has been isolated which proved to be identical with the new metabolite according to TIC, MS and NMR.     

Effect of acetylcholine on growth and isoperoxidases of the lentil(Lens culinaris) root

The effects of acetylcholine (Ach) on growth, the total peroxidase activity and the isoperoxidase spectrum of the roots ofLens culinaris were studied and compared with actual and earlier results obtained with an auxin (IAA) treatment. The general growth and peroxidase activity patterns of Ach treated roots and IAA treated ones showed many important similarities.     

Refractoriness of ovarian adenylate cyclase to continued hormonal stimulation.

Culture of preovulatory rat follicles with luteinizing hormone, follicle-stimulating hormone or prostaglandin E2 for 24 h reduced the subsequent response of adenylate cyclase to the homologous by 80, 50 and 90%, respectively; yet follicles refractory to luteinizing hormone fully responded to follicle-stimulating hormone responded to luteinizing hormone and prostaglandin E2, and those refractory to prostaglandin E2 could be stimulated by either gonadotropin. Desensitization of the adenylate cyclase system by luteinizing hormone was achieved by hormone concentrations of 0.8--2.0 mug/ml in the medium; a lower dose of luteinizing hormone (0.4 mug/ml), though effective in stimulating adenylate cyclase, did not induce refractoriness. Prostaglandin E2 caused partial refractoriness at dose levels of 0.1--0.25 mug/ml; higher dose levels were more effective. These findings suggest that continued exposure to the preovulatory follicle to elevated levels of hormones may cause perturbations in either the interaction between the hormone and its specific receptor or in a subsequent step essential for activation of adenylate cyclase.     

Ligand binding and enzymic catalysis coupled through subunits in tyrosyl-tRNA synthetase.

The interaction of the tyrosyl-tRNA synthetase from Bacillus stearothermophilus with its substrates in the aminoacyl adenylation reaction has been studied by stopped-flow fluorescence. The observed changes have been assigned to their chemical and physical processes by comparison with equilibrium dialysis, pyrophosphate exchange kinetics and rapid quenching and sampling techniques to give the rate constants for ligand binding, the formation of tyrosyl adenylate, and the reverse reaction. The stoichiometry of tyrosine and ATP binding in the catalytic process has been determined directly by equilibrium dialysis and equilibrium gel filtration under pyrophosphate exchange conditions, i.e., where a steady state has been set up in which the equilibrium position favors starting materials. It is shown that the rate-determining step in the formation of tyrosyl adenylate involves 1 mole each of tyrosine and ATP. A second mole of tyrosine and ATP bind to the aminoacyl adenylate complex stabilizing the high-energy intermediate. The enzyme tyrosyl adenylate complex that is isolated by gel filtration is in a different conformational state from that in the presence of tyrosine and ATP.