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Apparent Absence of a Translocase in the Cerebral Glucose‐6‐Phosphatase System
Author(s) -
Fishman Robert S.,
Karnovsky Manfred L.
Publication year - 1986
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1986.tb12978.x
Subject(s) - dids , biochemistry , microsome , translocase , endoplasmic reticulum , substrate (aquarium) , enzyme , chemistry , biology , membrane , ecology , chromosomal translocation , gene
In the hepatocyte endoplasmic reticulum, a substrate transporter could provide a means of regulating hydrolysis of glucose‐6‐phosphate by specifically modulating access of the substrate to the hydrolase. Several characteristics of the cerebral microsomal enzyme suggest that such an hypothesis is untenable in the brain. These are: (a) the inability of the enzyme in either untreated or detergent‐disrupted brain microsomes to distinguish between glucose‐6‐phosphate and mannose‐6‐phosphate; (b) the close agreement of the apparent K m values for either substrate in intact or disrupted microsomal preparations; (c) the constancy of the latency toward both substrates over a wide concentration range; (d) the inability of nonpenetrating, covalently‐linking reagents [e.g., 4,4′‐diisothiocyanostilbene‐2,2′‐disulfonic acid (DIDS)] to affect the accessibility of the hydrolase to its substrate; (e) the absence of a putative transporter polypeptide, such as that of the liver, in experiments where tritiated H 2 DIDS, polyacrylamide gel electrophoresis, and radioautography are applied to brain microsomes.