Table Of ContentContributors to Volume 11
MICHAEL S. BROWN
JOSEPH L. GOLDSTEIN
OSAMU HAYAISHI
HAROLD L. SEGAL
YUTAKA SHIZUTA
WILLY STALMANS
DAVID A. WALKER
SIDNEY WEINHOUSE
CURRENT TOPICS IN
Cellular Regulation
edited by
Bernard L Horecker · Earl R. Stadtman
Roche Institute of Molecular Biology National Institutes of Health
Nutley, New Jersey Bethesda, Maryland
Volume 1Ί-Ί976
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List of Contributors
Numbers in parentheses indicate the pages on which the authors' contributions begin.
MICHAEL S. BROWN (147), Division of Medical Genetics, Department of
Internal Medicine, University of Texas Health Science Center at
Dallas, Dallas, Texas
JOSEPH L. GOLDSTEIN (147), Division of Medical Genetics, Department of
Internal Medicine, University of Texas Health Science Center at
Dallas, Dallas, Texas
OSAMU HAYAISHI (99), Department of Medical Chemistry, Kyoto Uni
versity Faculty of Medicine, Kyoto, Japan
HAROLD L. SEGAL (183), Division of Cell and Molecular Biology, State
University of New York, Buffalo, New York
YUTAKA SHIZUTA (99), Department of Medical Chemistry, Kyoto Uni
versity Faculty of Medicine, Kyoto, Japan
WILLY STALMANS (51), Laboratoire de Chimie Physiologique, Universite
de Louvain, and International Institute of Cellular and Molecular
Pathology, Brussels, Belgium
DAVID A. WALKER (203), Department of Botany, The University of Shef
field, Sheffield, United Kingdom
SIDNEY WEINHOUSE (1), The Fels Research Institute, and the Department
of Biochemistry, Temple University School of Medicine, Philadel
phia, Pennsylvania
Vll
Preface
Recent years have witnessed rapid advances in our knowledge of the
basic mechanisms involved in the regulation of diverse cellular activities
such as intermediary metabolism, the transfer of genetic information,
membrane permeability, and cellular differentiation and other organ func
tions. Information gained from the detailed analyses of a large number
of isolated enzyme systems, together with results derived from physio
logical investigations of metabolic processes in vivo, constitutes an ever-
increasing body of knowledge from which important generalized concepts
and basic principles of cellular regulation are beginning to emerge. How
ever, so rapid are the present advances in the general area of cellular
regulation and so diverse are the disciplines involved, that it has become
a formidable task for even the expert in a specialized area to keep abreast
of the progress in his field. This series of volumes is concerned with such
recent developments in various areas of cellular regulation. We do not
intend that it will consist of comprehensive annual reviews of the litera
ture. We hope rather that it will constitute a medium which will, on the
one hand, provide contributing authors with an opportunity to summarize
progress in specialized areas of study that have undergone substantial
developments and, on the other hand, serve as a forum for the enunciation
of general principles and for the formulation of provocative theories and
novel concepts. To this end editorial review of individual contributions
will be concerned primarily with the clarity of presentation and con
formity to publication policies. It is hoped in this manner to bring together
current knowledge of various aspects of cellular regulation so as both to
enlighten the uninformed and to provide a base of knowledge for those
engaged in research in this subject.
BERNARD L. HORECKER
EARL R. STADTMAN
IX
Preface to Volume 11
Although physiologists have long been aware of the key role of the
liver in the homeostasis of blood glucose it is only recently that the details
of the underlying biochemical mechanisms have begun to emerge. Two
aspects of this important regulatory process are reviewed in the present
volume. The chapter on glucokinase, written by one of its discoverers,
develops current information on the properties of this enzyme, which is
now known to play a key role in glucose uptake by liver. The chapter
that follows presents a broad overview of the mechanisms that are be
lieved to control both glucose uptake by and release from the liver and
focuses attention on the enzymes involved in glycogen synthesis and
breakdown, where allosteric effects of glucose have recently been un
covered. Each of these chapters concludes with consideration of the cur
rent theories of the role of insulin in the regulation of glucose phos-
phorylation and in glycogenesis and glycogenolysis.
One of the classical enzyme models for allosteric regulatory mechanisms
is the biodegradative threonine deaminase. However, it has now become
apparent that neither the Monod nor the Koshland mechanism is entirely
consistent with the properties of this enzyme. The third chapter in this
volume expands on the subunit association-dissociation model for the
regulation of this enzyme that was proposed in an earlier volume. It is
suggested that some features of the model developed here may be appli
cable to other enzymes.
Another aspect of homeostasis, namely, the control of blood cholesterol
levels, is considered in the fourth chapter. A novel feature of the studies
reported is the use of cultured mammalian cells, in which cholesterol bio
synthesis has been shown to be controlled by the levels of cholesterol in
the growth medium. Studies of mutant cell lines have helped to elucidate
the pathway for the uptake, synthesis, and storage of cholesterol and
also have shed light on the nature of the regulatory mechanisms.
Early work on the control of intracellular enzyme levels was concerned
primarily with regulation of enzyme synthesis, and it is only recently that
the problem of enzyme degradation has begun to attract interest. In the
fifth chapter, a model for protein turnover is presented, based on the
theory that a particular conformer or conformational subspecies of the
protein is the form susceptible to lysosomal uptake and proteolytic attack.
Consideration is also given to other mechanisms for the selective degrada-
xi
Xll PREFACE TO VOLUME 11
tion of protein, including selective uptake by lysosomes and the possible
role of stabilizing factors.
The final chapter examines the complex regulatory mechanisms that
have been proposed for the regulation of photosynthetic carbon assimila
tion, including responses to changes in illumination, temperature, and
levels of C0 and orthophosphates. Among the mechanisms considered are
2
regulation of enzyme levels and activity, mass action, and intracellular
transport of intermediates, end-products and reducing power. This chapter
presents another point of view on the regulation of photosynthesis, which
has been the subject of earlier chapters in this series.
BERNARD L. HORECKER
EARL R. STADTMAN
Erratum
CURRENT TOPICS IN CELLULAR REGULATION
Volume 10
Page 248: The expression at the top of the page should read:
(3H in glucose + 3H in water)/3H in water
Xlll
Regulation of Glucokinase in Liver*
I SIDNEY WEINHOUSE
I The Fels Research Institute and the
I Department of Biochemistry
I Temple University School of
I Medicine
I Philadelphia, Pennsylvania
I. Introduction and History 1
A. Assay 2
B. Species Distribution 5
C. Purification and Properties 7
II. Localization in Hepatic Parenchymal Cells 11
III. Dietary Regulation 13
IV. Hormonal Regulation 16
A. Insulin 16
B. Interaction with Other Hormones 21
C. Adrenalectomy and Cortical Steroids 22
D. Hypophysectomy 24
E. Thyroid 27
F. Human Liver Responsiveness to Glucose and Insulin . . 28
V. Embryonic Development 29
VI. Phosphotransferase Activity of Glucose-6-phosphatase . .. 32
VII. Glucokinase in Regenerating Liver 34
Cell Culture Studies 35
VIII. Glucokinase in "Aged" Rats 35
IX. Glucokinase in Extrahepatic Tissue 38
A. Glucokinase in Intestinal Mucosa 39
B. Glucokinase in Liver Tumors 40
X. Possible Mechanisms of Insulin Action on Glucokinase . .. 41
References 45
I. Introduction and History
Glucokinase (EC 2.7.1.2) is a unique glucose-ATP phosphotransferase
with adaptive and kinetic properties that endow it with special physio
logical significance in the utilization of glucose by liver. The existence of
a hexokinase with unusual properties was foreshadowed by several puz
zling features of liver physiology. In contrast with muscle and adipose
* This review will be limited in scope to only the high K glucose-ATP phospho
m
transferase found in liver of many animal species, and will dwell mainly on regula
tory aspects. For a broader perspective on other hexokinase types, the reader is
referred to the comprehensive review by Walker (165). Further material will be
found in a recent review by Ureta (155a) on the phylogeny and ontogenesis of
vertebrate hexokinase.
1
2 SIDNEY WEINHOUSE
cells, which are normally impermeable to glucose and require insulin for
enhancement of its transport {89, 115), the liver cell is freely permeable
to the inward and outward flow of glucose {24). Nevertheless, experi
ments with liver slices indicated that insulin is necessary for proper util
ization of glucose by liver {26, 116, 146). Moreover, despite a reported
low K for glucose, of the order 10~7 to 10~5 for hitherto known hexoki-
m
nases {144, 165), and the free permeability of the liver cell toward this
sugar, glucose is taken up by liver only in the hyperglycemic condition.
Spiro {145) and Cahill et al. {25) observed that glucose uptake by liver
slices was highly dependent on the glucose concentration; and Spiro
calculated a "K " of 0.06 M for conversion of [14C] glucose to C0 .
m 2
These results pointed to a concentration-dependent early step in the
intracellular utilization of glucose. Any inferences from these data con
cerning the K for glucose phosphorylation in liver remained open to
m
question, however, because of the likelihood of a glucose concentration
gradient across the thickness of approximately 25 cells of the average
liver slice, as well as the complicating effects of glucose production, a
major function of liver; and the uncertainty introduced by the possibility
of isotope exchange reactions {60, 127). More definitive evidence for a
high "K " for conversion of [14C] glucose to C0 was obtained by Di-
m 2
Pietro, Sharma, and Weinhouse {39). In experiments with whole, forti
fied rat liver homogenates, they obtained a "K " of 10-20 ml for
m
[14C] glucose oxidation to 14C0 , whereas that for [14C] fructose oxidation
2
was below 2 ml, although the 7 for both sugars was similar. In the
max
same homogenates, oxidation of [14C]glucose-6-P at a concentration of
2 mM was 9 times higher than that of [14C] glucose at the same concen
tration, whereas at 14 mM, oxidation of both substrates was similar.
These results strongly pointed to the phosphorylation of glucose as the
concentration-dependent step in rat liver.
A. Assay
There is a long history of early inadequate and inconclusive attempts
to assay glucose phosphorylation in liver and other tissues, and to assess
hormonal effects thereon {19, 28, 73, 149, 175). These have been sum
marized by DiPietro {38). The available methodologies were unable to
cope with the complexities of the liver system, and it was not until an
enzymic procedure was developed for spectroscopic measurement of glu-
cose-6-P, the product of glucose phosphorylation, that serious effort
could be applied to the assay of hepatic glucose phosphorylation {38-40).
Vester {161), the first to measure glucose phosphorylation by coupling
with glucose-6-P dehydrogenase, found very low activities—no doubt
owing to an endogenous level of glucose-6-P dehydrogenase activity that
