Enzymatic Blocks Research Articles

Disorders of branched chain amino acid metabolism.

The three essential branched-chain amino acids (BCAAs), leucine, isoleucine and valine, share the first enzymatic steps in their metabolic pathways, including a reversible transamination followed by an irreversible oxidative decarboxylation to coenzyme-A derivatives. The respective oxidative pathways subsequently diverge and at the final steps yield acetyl- and/or propionyl-CoA that enter the Krebs cycle. Many disorders in these pathways are diagnosed through expanded newborn screening by tandem mass spectrometry. Maple syrup urine disease (MSUD) is the only disorder of the group that is associated with elevated body fluid levels of the BCAAs. Due to the irreversible oxidative decarboxylation step distal enzymatic blocks in the pathways do not result in the accumulation of amino acids, but rather to CoA-activated small carboxylic acids identified by gas chromatography mass spectrometry analysis of urine and are therefore classified as organic acidurias. Disorders in these pathways can present with a neonatal onset severe-, or chronic intermittent- or progressive forms. Metabolic instability and increased morbidity and mortality are shared between inborn errors in the BCAA pathways, while treatment options remain limited, comprised mainly of dietary management and in some cases solid organ transplantation.

Leucine Biosynthesis Regulates Cytoplasmic Iron-Sulfur Enzyme Biogenesis in an Atm1p-independent Manner

Fe-S clusters (ISCs) are versatile cofactors utilized by many mitochondrial, cytoplasmic, and nuclear enzymes. Whereas mitochondria can independently initiate and complete ISC synthesis, other cellular compartments are believed to assemble ISCs from putative precursors exported from the mitochondria via an ATP binding cassette (ABC) transporter conserved from yeast (Atm1p) to humans (ABCB7). However, the regulatory interactions between mitochondrial and extramitochondrial ISC synthesis are largely unknown. In yeast, we found that mitochondrial ISC synthesis is regulated by the leucine biosynthetic pathway, which among other proteins involves an abundant cytoplasmic [4Fe-4S] enzyme, Leu1p. Enzymatic blocks in the pathway (i.e. leu1Δ or leu2Δ gene deletion mutations) induced post-transcriptional up-regulation of core components of mitochondrial ISC biosynthesis (i.e. the sulfur donor Nfs1p, the iron donor Yfh1p, and the ISC scaffold Isu1p). In leu2Δ cells, transcriptional mechanisms also led to dramatic up-regulation of Leu1p with concomitant down-regulation of mitochondrial aconitase (Aco1p), a [4Fe-4S] enzyme in the tricarboxylic acid cycle. Accordingly, the leu2Δ deletion mutation exacerbated Aco1p inactivation in cells with mutations in Yfh1p. These data indicate that defects in leucine biosynthesis promote the biogenesis of enzymatically active Leu1p at the expense of Aco1p activity. Surprisingly, this effect is independent of Atm1p; previous reports linking the loss of Leu1p activity to Atm1p depletion were confounded by the fact that LEU2 was used as a selectable marker to create Atm1p-depleted cells, whereas a leu2Δ allele was present in Atm1p-repleted controls. Thus, still largely unknown transcriptional and post-transcriptional mechanisms control ISC distribution between mitochondria and other cellular compartments.

UV-induced galactose-negative mutants of Ophiostoma multiannulatum

In order to study the significance of the proposed galactose-pentose pathway for galactose metabolism in Ophiostoma multiannulatum (Lindberg 1970 b) we prepared a strain which had both this and the Leloir pathway functioning. UV was used for induction of mutations in the genes controlling enzymes of the Leloir pathway. Two mutants with enzymatic blocks in the Leloir pathway were isolated. The mutants were phenotypically characterized and it was concluded that the galactose-pentose pathway is only of minor importance in Ophiostoma as compared to the Leloir pathway.

Restoration of Gibberellin Production in Fusarium proliferatum by Functional Complementation of Enzymatic Blocks

Nine biological species, or mating populations (MPs), denoted by letters A to I, and at least 29 anamorphic Fusarium species have been identified within the Gibberella fujikuroi species complex. Members of this species complex are the only species of the genus Fusarium that contain the gibberellin (GA) biosynthetic gene cluster or at least parts of it. However, the ability of fusaria to produce GAs is so far restricted to Fusarium fujikuroi, although at least six other MPs contain all the genes of the GA biosynthetic gene cluster. Members of Fusarium proliferatum, the closest related species, have lost the ability to produce GAs as a result of the accumulation of several mutations in the coding and 5' noncoding regions of genes P450-4 and P450-1, both encoding cytochrome P450 monooxygenases, resulting in metabolic blocks at the early stages of GA biosynthesis. In this study, we have determined additional enzymatic blocks at the first specific steps in the GA biosynthesis pathway of F. proliferatum: the synthesis of geranylgeranyl diphosphate and the synthesis of ent-kaurene. Complementation of these enzymatic blocks by transferring the corresponding genes from GA-producing F. fujikuroi to F. proliferatum resulted in the restoration of GA production. We discuss the reasons for Fusarium species outside the G. fujikuroi species complex having no GA biosynthetic genes, whereas species distantly related to Fusarium, e.g., Sphaceloma spp. and Phaeosphaeria spp., produce GAs.

Recognition and management of fatty acid oxidation defects: a series of 107 patients.

In a personal series of 107 patients, we describe clinical presentations, methods of recognition and therapeutic management of inherited fatty acid oxidation (FAO) defects. As a whole, FAO disorders appear very severe: among the 107 patients, only 57 are still living. Including 47 siblings who died early in infancy, in total 97 patients died, of whom 30% died within the first week of life and 69% before 1 year. Twenty-eight patients presented in the neonatal period with sudden death, heart beat disorders, or neurological distress with various metabolic disturbances. Hepatic presentations were observed in 73% of patients (steatosis, hypoketotic hypoglycaemia, hepatomegaly, Reye syndrome). True hepatic failure was rare (10%); cholestasis was observed in one patient with LCHAD deficiency. Cardiac presentations were observed in 51% of patients: 67% patients presented with cardiomyopathy, mostly hypertrophic, and 47% of patients had heart beat disorders with various conduction abnormalities and arrhythmias responsible for collapse, near-miss and sudden unexpected death. All enzymatic blocks affecting FAO except CPT I and MCAD were found associated with cardiac signs. Muscular signs were observed in 51% of patients (of whom 64% had myalgias or paroxysmal myoglobinuria, and 29% had progressive proximal myopathy). Chronic neurologic presentation was rare, except in LCHAD deficiency (retinitis pigmentosa and peripheral neuropathy). Renal presentation (tubulopathy) and transient renal failure were observed in 27% of patients. The diagnosis of FAO disorders is generally based on the plasma acylcarnitine profile determined by FAB-MS/MS from simple blood spots collected on a Guthrie card. Urinary organic acid profile and total and free plasma carnitine can also be very helpful, mostly in acute attacks. If there is no significant disturbance between attacks, the diagnosis is based upon a long-chain fatty acid loading test, fasting test, and in vitro studies of fatty acid oxidation on fresh lymphocytes or cultured fibroblasts. Treatment includes avoiding fasting or catabolism, suppressing lipolysis, and carnitine supplementation. The long-term dietary therapy aims to prevent periods of fasting and restrict long-chain fatty acid intake with supplementation of medium-chain triglycerides. Despite these therapeutic measures, the long-term prognosis remains uncertain.

Diet change in the management of metabolic encephalomyopathies.

Dietary treatment of mitochondrial disease caused by oxidative metabolic defects has traditionally been limited to the use of ketogenic diets for the treatment of pyruvate dehydrogenase (PDH) deficiency. However, defects in mitochondrial function resulting in a failure of oxidative metabolism can result in a block in the utilization of various food substrates and dietary manipulation might be beneficial. Certain predictions might be made based on the site of particular enzymatic blocks. Some disorders primarily block a particular substrate pathway, such as PDH deficiency which predominantly affects the utilization of carbohydrates and acyl-CoA dehydrogenase deficiencies which predominantly affect fat metabolism. Defects of the terminal electron transport chain, ubiquinone to cytochrome oxidase (COX), affect the ‘final common pathway’ for energy production and might be expected to impair the utilization of all food substrates. In complex I deficiency utilization of carbohydrates which generate NADH, might be expected to be impaired. The β-oxidation of fats produces NADH, ETFred and acetyl-CoA. Reducing equivalents derived from β-oxidation enter the electron transport chain at both site 1 (complex I) and site 2 (ubiquinone). Electron transport defects involving complex I may theoretically benefit from the use of high fat diets as reducing equivalents from ETFred can be introduced through the ETF/ubiquinone pathway from the metabolism of fatty acids. In patients whose lactic acid production is increased by carbohydrate intake, fructose, which is rapidly metabolized to pyruvate, might be less well tolerated than glucose as a food source.

Testicular function in prepubertal male pseudohermaphroditism.

Testicular function was evaluated in forty-one prepubertal patients with male pseudohermaphroditism by determining serum concentrations of progesterone, 17-hydroxyprogesterone, dehydroepiandrosterone, androstenedione, testosterone and dihydrotestosterone before and after stimulation with hCG and, in some instances, ACTH. Testosterone response to hCG was normal in all subjects. In one patient, a 4-year-old boy, a deficiency of 17,20-desmolase activity was diagnosed based on the coexistence of elevated levels of pregnenolone, 17-hydroxypregnenolone, progesterone and 17-hydroxyprogesterone and low levels of dehydroepiandrosterone and androstenedione. In three other patients enzymatic blocks were suspected but not confirmed. Congenital deficiency of enzymes necessary for testosterone biosynthesis is an uncommon aetiology of male pseudohermaphroditism.

Loosely coupled mitochondrial oxidative phosphorylation induced by protoporphyrin

Protoporphyrin induces loose coupling in rat liver mitochondria at concentrations probably encountered in porphyric patients. Features of porphyric crises suggesting acute mitochondrial dysfunction are reviewed. Porphyrins which accumulate behind enzymatic blocks may produce crises by secondarily altering mitochondrial respiration.

ENZYMATIC MECHANISMS IN PORPHYRIN SYNTHESIS: POSSIBLE ENZYMATIC BLOCKS IN PORPHYRIAS*

Annals of the New York Academy of SciencesVolume 104, Issue 2 p. 676-688 ENZYMATIC MECHANISMS IN PORPHYRIN SYNTHESIS: POSSIBLE ENZYMATIC BLOCKS IN PORPHYRIAS* Lawrence Bogorad, Lawrence Bogorad Department of Botany, University of Chicago, Chicago, Ill.Search for more papers by this author Lawrence Bogorad, Lawrence Bogorad Department of Botany, University of Chicago, Chicago, Ill.Search for more papers by this author First published: March 1963 https://doi.org/10.1111/j.1749-6632.1963.tb17701.xCitations: 43 * This work was supported by grants from the National Institute of Arthritis and Metabolic Diseases, United States Public Health Service (A-1010), and the National Science Foundation. It was also supported in part by the Dr. Wallace C. and Clara A. Abbott Memorial Fund of the University of Chicago. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume104, Issue2Some Aspects of Metabolic Diseases in Man and AnimalsMarch 1963Pages 676-688 RelatedInformation

Essential amino acids and disease processes. II. Psoriasis and pityriasis rubra pilaris.

Amino acids are involved in many systemic disease processes and also in various disorders where the skin presents most or all of the pathology. 1 The intermediary metabolism of amino acids consists of a series of well-defined chemical reactions. Each reaction is catalyzed and controlled by a system of enzymes, and these enzymes are made by tissue cells in a manner related to genes and heredity. If such an enzyme system is lacking or defective, this constitutes an inborn error of metabolism and can bring about profound changes in the normal metabolic chain of reactions, with utilization of alternate and unusual metabolic pathways and accumulation of disease-producing metabolites. With phenylalanine, enzymatic defects, metabolic blocks, and accumulation of toxic metabolites occur at 3 separate steps in the usual metabolic reaction chain, resulting in 3 separate disorders-phenylpyruvic oligophrenia, alkaptonuria, and tyrosinosis. Also, specific enzymatic blocks in metabolism of other amino acids are

DISORDERS ASSOCIATED WITH THE METABOLISM OF PHENYLALANINE AND TYROSINE

DISORDERS ASSOCIATED WITH THE METABOLISM OF PHENYLALANINE AND TYROSINE