Increased PRPP synthetase activity in cultured rat hepatoma cells containing mutations in the hypoxanthine guanine phosphoribosyltransferase gene

L. Gráf, J. A. McRoberts, T. M. Harrison, D. W. Martin

Research output: Article

12 Citations (Scopus)

Abstract

Nine independently derived clones of mutagenized rat hepatoma cells selected for resistance to 6 mercaptopurine (6 MP) or 6 thioguanine (6 ThioG) have been isolated. Each has severely reduced catalytic activity of hypoxanthine guanine phosphoribosyltransferase (HPRT) and seven of them possess significantly increased activities of phosphoribosylpyrophosphate (PRPP) synthetase. The degrees of elevations of PRPP synthetase activities do not correlate with the degrees of deficiencies of HPRT activities. The cells from one of these clones, 1020/12, possess 40% of the normal HPRT catalytic activity and overproduce purines. We have extensively examined the cells from this clone. Immunotitration studies of 1020/12 cells indicate that there is a mutation in the structural gene for HPRT. Although they possess increased specific catalytic activities of the enzyme, PRPP synthetase, the catalytic parameters, heat stability, and isoelectric pH of PRPP synthetase from 1020/12 cells are indistinguishable from those of the enzyme from wild type cells. The cause of purine overproduction by 1020/12 cells appears to be the elevated PRPP synthetase activity, rather than a PRPP 'sparing' effect stemming from reduced HPRT activity. Support for this idea is provided by the observation that the complete loss of HPRT activity in a clone derived from 1020/12 cells does not further enhance the levels of PRPP synthetase or purine overproduction. We propose that the elevated levels of PRPP synthetase activity in these HPRT deficient cells result from a mutational event in the structural gene for HPRT, and that this causes the disruption of a previously undescribed regulatory function of this gene on the expression of the PRPP synthetase gene.

Original languageEnglish
Pages (from-to)331-342
Number of pages12
JournalJournal of Cellular Physiology
Volume88
Issue number3
Publication statusPublished - 1976

Fingerprint

Ribose-Phosphate Pyrophosphokinase
Hypoxanthine Phosphoribosyltransferase
Rats
Hepatocellular Carcinoma
Genes
Mutation
Clone Cells
Catalyst activity
Lesch-Nyhan Syndrome
Thioguanine
6-Mercaptopurine
Purines
Enzymes
Regulator Genes
Hot Temperature

ASJC Scopus subject areas

  • Cell Biology
  • Clinical Biochemistry
  • Physiology

Cite this

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title = "Increased PRPP synthetase activity in cultured rat hepatoma cells containing mutations in the hypoxanthine guanine phosphoribosyltransferase gene",
abstract = "Nine independently derived clones of mutagenized rat hepatoma cells selected for resistance to 6 mercaptopurine (6 MP) or 6 thioguanine (6 ThioG) have been isolated. Each has severely reduced catalytic activity of hypoxanthine guanine phosphoribosyltransferase (HPRT) and seven of them possess significantly increased activities of phosphoribosylpyrophosphate (PRPP) synthetase. The degrees of elevations of PRPP synthetase activities do not correlate with the degrees of deficiencies of HPRT activities. The cells from one of these clones, 1020/12, possess 40{\%} of the normal HPRT catalytic activity and overproduce purines. We have extensively examined the cells from this clone. Immunotitration studies of 1020/12 cells indicate that there is a mutation in the structural gene for HPRT. Although they possess increased specific catalytic activities of the enzyme, PRPP synthetase, the catalytic parameters, heat stability, and isoelectric pH of PRPP synthetase from 1020/12 cells are indistinguishable from those of the enzyme from wild type cells. The cause of purine overproduction by 1020/12 cells appears to be the elevated PRPP synthetase activity, rather than a PRPP 'sparing' effect stemming from reduced HPRT activity. Support for this idea is provided by the observation that the complete loss of HPRT activity in a clone derived from 1020/12 cells does not further enhance the levels of PRPP synthetase or purine overproduction. We propose that the elevated levels of PRPP synthetase activity in these HPRT deficient cells result from a mutational event in the structural gene for HPRT, and that this causes the disruption of a previously undescribed regulatory function of this gene on the expression of the PRPP synthetase gene.",
author = "L. Gr{\'a}f and McRoberts, {J. A.} and Harrison, {T. M.} and Martin, {D. W.}",
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T1 - Increased PRPP synthetase activity in cultured rat hepatoma cells containing mutations in the hypoxanthine guanine phosphoribosyltransferase gene

AU - Gráf, L.

AU - McRoberts, J. A.

AU - Harrison, T. M.

AU - Martin, D. W.

PY - 1976

Y1 - 1976

N2 - Nine independently derived clones of mutagenized rat hepatoma cells selected for resistance to 6 mercaptopurine (6 MP) or 6 thioguanine (6 ThioG) have been isolated. Each has severely reduced catalytic activity of hypoxanthine guanine phosphoribosyltransferase (HPRT) and seven of them possess significantly increased activities of phosphoribosylpyrophosphate (PRPP) synthetase. The degrees of elevations of PRPP synthetase activities do not correlate with the degrees of deficiencies of HPRT activities. The cells from one of these clones, 1020/12, possess 40% of the normal HPRT catalytic activity and overproduce purines. We have extensively examined the cells from this clone. Immunotitration studies of 1020/12 cells indicate that there is a mutation in the structural gene for HPRT. Although they possess increased specific catalytic activities of the enzyme, PRPP synthetase, the catalytic parameters, heat stability, and isoelectric pH of PRPP synthetase from 1020/12 cells are indistinguishable from those of the enzyme from wild type cells. The cause of purine overproduction by 1020/12 cells appears to be the elevated PRPP synthetase activity, rather than a PRPP 'sparing' effect stemming from reduced HPRT activity. Support for this idea is provided by the observation that the complete loss of HPRT activity in a clone derived from 1020/12 cells does not further enhance the levels of PRPP synthetase or purine overproduction. We propose that the elevated levels of PRPP synthetase activity in these HPRT deficient cells result from a mutational event in the structural gene for HPRT, and that this causes the disruption of a previously undescribed regulatory function of this gene on the expression of the PRPP synthetase gene.

AB - Nine independently derived clones of mutagenized rat hepatoma cells selected for resistance to 6 mercaptopurine (6 MP) or 6 thioguanine (6 ThioG) have been isolated. Each has severely reduced catalytic activity of hypoxanthine guanine phosphoribosyltransferase (HPRT) and seven of them possess significantly increased activities of phosphoribosylpyrophosphate (PRPP) synthetase. The degrees of elevations of PRPP synthetase activities do not correlate with the degrees of deficiencies of HPRT activities. The cells from one of these clones, 1020/12, possess 40% of the normal HPRT catalytic activity and overproduce purines. We have extensively examined the cells from this clone. Immunotitration studies of 1020/12 cells indicate that there is a mutation in the structural gene for HPRT. Although they possess increased specific catalytic activities of the enzyme, PRPP synthetase, the catalytic parameters, heat stability, and isoelectric pH of PRPP synthetase from 1020/12 cells are indistinguishable from those of the enzyme from wild type cells. The cause of purine overproduction by 1020/12 cells appears to be the elevated PRPP synthetase activity, rather than a PRPP 'sparing' effect stemming from reduced HPRT activity. Support for this idea is provided by the observation that the complete loss of HPRT activity in a clone derived from 1020/12 cells does not further enhance the levels of PRPP synthetase or purine overproduction. We propose that the elevated levels of PRPP synthetase activity in these HPRT deficient cells result from a mutational event in the structural gene for HPRT, and that this causes the disruption of a previously undescribed regulatory function of this gene on the expression of the PRPP synthetase gene.

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