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At least 343 records · Page 19Linked to original sources
PubMed1980

The synthesis and properties of 4,5-dioxovaleric acid, a possible intermediate in the biosynthesis of 5-aminolaevulinic acid, and its in vivo formation in Scenedesmus obliquus.

The formation of 5-aminolaevulinic acid for chlorophyll biosynthesis in the pigment mutant C-2A' of the unicellular green alga Scenedesmus obliquus occurs via two pathways: the first and major pathway uses glycine and succinyl-CoA as precursors and the second, the C-5 pathway, uses the intact five C-atom skeleton of either glutamate or 2-oxoglutarate. The intermediates in this latter pathway of 5-aminolaevulinic acid biosynthesis are still a matter of controversy and discussion but, in this paper, we have demonstrated in this Scenedesmus mutant that 4,5-dioxovaleric acid occurs in the cells when illuminated in the presence of laevulinic acid and the amount of 4,5-dioxovaleric acid formed is dependent on the period of illumination. In a preliminary experiment we have shown, under similar conditions, that labelled 4,5-dioxovaleric acid can be obtained from both DL-[1-(14)C]glutamate and [2-(14)C]glycine. This suggests that 4,5-dioxovaleric acid is formed enzymically from the intact five C-atom skeleton of glutamate but may also arise from the deamination of ALA formed by the condensation of succinyl-CoA and glycine by the 5-aminolaevulinic acid synthase pathway. To obtain positive identification the naturally occurring, and also the labelled, 4,5-dioxovaleric acid were isolated as the more stable benzoquinoxaline derivative by condensation with 2,3-diaminonaphthalene and identified by comparison with the benzoquinoxaline derivative of an authentic sample of 4,5-dioxovaleric acid prepared by the hydrogenation of the ozonide of benzylidene laevulinic acid. The structures of the authentic sample of 4,5-dioxovaleric acid and its benzoquinoxaline derivative were confirmed by NMR and mass spectroscopy and both were further characterized by TLC and by infrared, ultraviolet and fluorescence spectroscopy.

Aminolevulinic Acid↗
PubMed1988

Formation of 5-aminolevulinate via glutamate-1-semialdehyde and 4,5-dioxovalerate with participation of an RNA component in Scenedesmus obliquus mutant C-2A'.

In the yellow mutant C-2A' of the unicellular green alga Scenedesmus obliquus the participation of an RNA species in the conversion of glutamate to 5-aminolevulinate is clearly demonstrated by the fact that RNAase treatment of a soluble enzyme preparation drastically decreases the formation of 5-aminolevulinate. The involvement of 4,5-dioxovalerate in the C5 pathway is demonstrated by the decrease of label in enzymatically formed 5-aminolevulinate from [14C]glutamate by providing an increased unlabelled pool of 4,5-dioxovalerate. Evidence supporting the role of glutamate-1-semialdehyde as an additional intermediate in the reaction sequence is also presented. We propose a new reaction scheme, consistent with the results reported here, for the formation of 5-aminolevulinate via the C5 pathway.

Aminolevulinic Acid↗
PubMed1973

gamma,delta-Dioxovalerate as a substrate for the glyoxalase enzyme system.

1. Crude gammadelta-dioxovalerate was synthesized from laevulinate by two different methods and was purified by Sephadex chromatography. Some analytical reactions of the compound are described. 2. gammadelta-Dioxovalerate is a substrate for glyoxalase I and the GSH derivative formed by this enzyme is hydrolysed by glyoxalase II to form d-alpha-hydroxyglutarate. The K(m) of glyoxalase I for gammadelta-dioxovalerate is 1.0x10(-3)m at pH5.8.3. The u.v.-absorption spectrum of thiol ester, synthesized enzymically from gammadelta-dioxovalerate and GSH by glyoxalase I, is almost identical with that for S-lactoylglutathione. Some optical properties of this thiol ester were measured. 4. Attempts to show reversibility of the glyoxalase system reactions with d-alpha-hydroxyglutarate as substrate were unsuccessful. 5. The possible metabolic role of the gammadelta-dioxovalerate reaction is discussed. It is suggested that one of the metabolic functions of the glyoxalase system may be to provide a mechanism for the entry of this compound into the tricarboxylic acid cycle.

Aldehydes↗
PubMed1976

Selective modification of rabbit muscle pyruvate kinase by 5-chloro-4-oxopentanoic acid.

Rabbit muscle pyruvate kinase was irreverisbly inactivated by 5-chloro-4-oxopentanoic acid with a pKa of 9.2. The inhibition was time-dependent and was related to the 5-chloro-4-oxopentanoic acid concentration. Analysis of the kinetics of inhibition showed that the binding of the inhibitor showed positive co-operativity (n = 1.5 +/- 0.2). Inhibition of pyruvate kinase by 5-chloro-4-oxopentanoic acid was prevented by ligands which bind to the active site. Their effectiveness was placed in the order Mg2+ greater than phosphoenolpyruvate greater than ATP greater than ADP greater than pyruvate. Inhibitor-modified pyruvate kinase was unable to catalyse the detritiation of [3-(3)H]pyruvate in the ATP-promoted reaction, but it did retain 5-10% of the activity with either phosphate or arsenate as promoters. 5-Chlor-4-oxo-[3,5-(3)H]pentanoic acid was covalently bound to pyruvate kinase and demonstrated a stoicheiometry of 1 mol of inhibitor bound per mol of pyruvate kinase protomer. The incorporation of the inhibitor and the loss of enzyme was proportional. These results are discussed in terms of 5-chloro-4-oxopentanoic acid alkylating a functional group in the phosphoryl overlap region of the active site, and a model is presented in which this compound alkylates an active-site thiol in a reaction that is controlled by a more basic group at the active site.

Alkylation↗
PubMed1979

Inhibition of amino acid transport into lymphoid cells by the glutamine analog L-2-amino-4-oxo-5-chloropentanoate.

Transport of L-glutamine and of the chloroketone glutamine analog L-2-amino-4-oxo-5-chloropentanoate into lymphoid cells is mediated by the same system. Arginine and a number of other amino acids (e.g., glutamate, aspartate, and lysine) are transported to a much lesser extent by this system. However, after uptake of the chloroketone into the cells, the transport of glutamine, arginine, and other amino acids is markedly inhibited, due evidently to reaction of the chloroketone with intracellular components that are involved in amino acid transport. The chloroketone acts more effectively on growing than on resting cells. Treatment of lymphoid cells with the chloroketone or with L-chloro-2,4-dinitrobenzene leads to rapid and complete depletion of intracellular glutathione without affecting cell viability. These reagents appear to be useful experimental tools for studies of glutathione function and metabolism.

Amino Acids↗
PubMed1980

[Normal levels of delta-aminolevulinic acid in the spot urines of adult men, as measured by a simplified method (author's transl)].

Increased urinary excretion of delta-aminolevulinic acid (ALA) is an early biological sign of toxic lead absorption. Therefore, its determination is a very useful screening test for the periodical examination of workers exposed to lead. Previously, we developed a simplified method for determining urinary ALA without ion-exchange column. This method is based on two findings: (a) ALA-pyrrole is extractable with ethyl acetate to be separated from other Ehrlich-positive substances such as urea, and (b) the ALA-pyrrole can form a complex with the modified Ehrlich's reagent in ethyl acetate. In the present study, using this method, we determined urinary ALA of healthy adult men and estimated the normal levels for ALA. The results are as follows: (1) The urinary ALA concentration obtained from the spot urine samples of 299 workers (age: mean=37.1 years range=20-56 years) with no history of occupational lead exposure was 2.39 +/- 0.87 mg/liter (mean and standard deviation), with upper limit of 4.10 mg/liter for 95%-confidence interval. (2) The distribution of ALA in the normal spot urine was not log-normal, but normal. (3) No significant difference between the excretion level of urinary ALA and the age was observed.

Adult↗