Regulation of hypoxia-inducible factor 1 by prolyl and asparaginyl hydroxylases

Hypoxia-inducible factor 1 (HIF-1) functions as a master regulator of oxygen homeostasis by mediating a wide range of cellular and systemic adaptive physiological responses to reduced oxygen availability. In this review, we will summarize recent progress in elucidating the molecular mechanisms of HIF-1 activation, focusing on the role of oxygen-dependent prolyl and asparaginyl hydroxylases in hypoxia signal transduction.     

Substrate specificity of the paraffin hydroxylase ofPseudomonas aeruginosa

The paraffin hydroxylating enzyme system isolated fromPseudomonas aeruginosa (strain 473) grown onn-heptane has been studied with respect to its substrate specificity. It has been found that cell-free extracts of this organism can hydroxylate a wide variety of hydrocarbons. In order to function as substrates, molecules should be able to assume a more or less planar conformation. The compounds used in this study can be divided into three classes: (a) alkanes, (b) alkylbenzenes and (c) (alkyl)cycloalkanes. In each of these groups hydroxylation occurs at a specific site in the molecule. Noteworthy is the hydroxylation of isopropyl groups at a methyl carbon and that of monoalkylcyclohexanes at the 4-transposition.From the geometry of the substrate and non-substrate molecules the conclusion was drawn that the active centre of the hydroxylase is a cleft in the enzyme surface of about 5 Å wide and 8 Å deep.We gratefully acknowledge the skillfull assistance of Miss W. T. Hempel.     

Cofactor and substrate requirements of collagen proline hydroxylase

Enzyme fractions which catalyze the hydroxylation of peptidyl-proline to form peptidyl-hydroxyproline have been prepared from chick embryo, guinea-pig granuloma and fetal rat skin. In all preparations ferrous ion, ascorbic acid, α-ketoglutarate and molecular oxygen are required for activity. No compounds have been found which can replace ferrous ion and α-ketoglutarate. Reduced pteridines can partially replace ascorbic acid, but reduced pyridine nucleotides are inactive. The enzyme has been called collagen proline hydroxylase and has been tentatively classified as a mixed-function oxidase. A formulation of the reaction catalyzed by this enzyme has been proposed in which ascorbate functions as a reducing agent and α-ketoglutarate as a modifier of the enzyme.