Linked Life Data

8299570

Source:http://linkedlifedata.com/resource/pubmed/id/8299570

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
2
pubmed:dateCreated
1994-3-8
pubmed:abstractText
3 beta-Hydroxy-5-ene-steroid dehydrogenase/delta 5-delta 4-isomerase (3 beta HSD) is a NAD(+)-dependent membrane-bound enzyme that catalyzes the oxidation of delta 5-3 beta-hydroxysteroids to delta 4-3-keto structures during adrenal, gonadal, and placental steroidogenesis. Enzyme activity is located in both microsomes and mitochondria. In these experiments we examined the membrane topologies of 3 beta HSD in rat and calf adrenal microsomes and mitochondria by comparing access to the active sites of coenzyme and the inhibitor mersalyl, a nonpenetrant organic mercurial anion. Microsomal activity required exogenous NAD+ and was inhibited by mersalyl, indicating that the active site faced the medium in vitro and the cytoplasm in vivo. In contrast, mitochondrial 3 beta HSD used matrix space NAD+, was inhibited by reduction of intramitochondrial NAD(P)+, and was insensitive to mersalyl. Mitochondrial activity was decreased by exogenous NADH (apparent Ki, 2.8 microM) and increased by added NAD+ (apparent Ka, 2.4 microM). However, mersalyl blocked the effects of exogenous NADH and NAD+ and returned the activity to that observed before coenzyme addition. The membrane-sidedness of the NAD+ activation was examined further in submitochondrial particles prepared by sonication of pyridine nucleotide-depleted calf adrenal cortex mitochondria. Particles were prepared in the absence or presence of 10 mM NAD+ and contained none or 2.9-7.3 nmol NAD+/mg protein, respectively. Both groups of submitochondrial particles required exogenous NAD+ for 3 beta HSD activity, indicating that the active site faced the medium (the particles were everted), and the contained NAD+ was inside the particles. However, 3 beta HSD activity was increased 12-140% in particles that contained NAD+. The results suggest that mitochondrial 3 beta HSD is an integral inner membrane protein, that the active site faces the matrix space and is influenced by coenzyme availability, and that a regulatory site(s) faces the intermembrane space. Binding of NAD+ or NADH to this external site increases or decreases, respectively, the rate of catalysis at the active site. Mitochondrial 3 beta HSD activity may be enhanced by oxidation of intermembrane space NADH via an active rotenone- and antimycin-a-insensitive NADH oxidase.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
AIM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Feb
pubmed:issn
0013-7227
pubmed:author
pubmed:issnType
Print
pubmed:volume
134
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
751-9
pubmed:dateRevised
2007-11-14
pubmed:meshHeading
pubmed:year
1994
pubmed:articleTitle
Topology of 3 beta-hydroxy-5-ene-steroid dehydrogenase/delta 5-delta 4-isomerase in adrenal cortex mitochondria and microsomes.
pubmed:affiliation
Institute for Medical Research, Mary Imogene Bassett Hospital, Cooperstown, New York 13326.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S., Research Support, Non-U.S. Gov't