Studies on rabbit liver phosphoglucomutase

Jamil, Haris

(1983)

Jamil, Haris (1983) Studies on rabbit liver phosphoglucomutase.

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Abstract

Phosphoglucomutases from different sources exhibit a variety of kinetic behaviour though it is probable they all have a common phosphoenzyme mechanism. The variations in behaviour arise partly from an intrinsic diphosphatase activity, which, even when present as a minor component, can affect the initial velocity patterns. Only isotopic induced-transport tests distinguish unequivocally between possible mechanisms. Rabbit liver phosphoglucomutase has a substantial amount of an isoenzyme, which appears to be associated with a high intrinsic diphosphatase activity. This activity may be involved in modulation of the glucose-1,6-diP level in the liver and hence in the regulation of carbohydrate metabolism.

A procedure for the isolation of comparatively undegraded phosphoglucomutase (mol. wt. 67,600) from rabbit liver with high specific activity is described. The purified preparation showed a low diphosphatase activity. Kinetic studies, using a sensitive fluorimetric assay at ionic strength 0.05 mol 1-1 and Mg++ free = 2.0 mM, give a parallel line initial velocity pattern. This behaviour is consistent with the phosphoenzyme mechanism. The liver enzyme indicated a higher Km for glucose-1,6-diP than many other phosphoglucomutases. Induced transport tests using 14C- and 32P-labelled substrates showed that the enzyme can only have a phosphoenzyme mechanism. The isolation of 32P-labelled phosphoenzyme which rapidly exchanged more than 95% of its 32P-label with substrates confirmed that this phosphoenzyme is a true kinetic intermediate in the mutase reaction. Labelled phosphoenzyme contained 0.45-0.6 mol 32P mol-1 enzyme and its half-life was 47.5 h at 30 °C. Evidence is presented that the phosphate is bound to a serine residue of the enzyme.

It is concluded that the low diphosphatase activity associated with the enzyme does not significantly modulate the level of glucose-1,6-diP in liver. Moreover, other factors must be responsible for the failure to isolate a completely phosphorylated phosphoenzyme. Although this phosphoglucomutase has a relatively high Km for glucose-1,6-diP, the known fluctuations in the level of glucose-1,6-diP in the liver are unlikely to affect phosphogluco-mutase activity.

Information about this Version

This is a Accepted version
This version's date is: 1983
This item is not peer reviewed

Link to this Version

https://repository.royalholloway.ac.uk/items/369683e3-7721-4bdb-bc8d-6b31ba2f1842/1/

Item TypeThesis (Doctoral)
TitleStudies on rabbit liver phosphoglucomutase
AuthorsJamil, Haris
Uncontrolled KeywordsBiochemistry; Pure Sciences; Liver; Phosphoglucomutase; Rabbit; Rabbit Liver; Rabbit Liver; Studies
DepartmentsDepartment of Biochemistry

Identifiers

ISBN978-1-339-62521-8

Deposited by () on 01-Feb-2017 in Royal Holloway Research Online.Last modified on 01-Feb-2017

Notes

Digitised in partnership with ProQuest, 2015-2016. Institution: University of London, Bedford College (United Kingdom).


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