Download The Interaction of Hydrogen Ions and Calcium Ions on the ATPase

Medical Research Society
The significance of these results will be discussed in
relation to specific features of the marrow depression
caused by these drugs.
12. IMMUNOCHEMICAL STUDIES OF MAMMALIAN GLYCOPROTEINS WITH BLOOD
GROUP I ACTIVITY
T. FEIZI
Division of Communicable Diseases, MRC Clinical
Research Centre, Warford Road, Harrow, Middlesex
HA1 3UJ
(Introduced by A. S. TAVILL)
The blood group I antigen is present on the erythrocytes of the vast majority of adults. Antibodies
directed against this antigen may give rise to autoimmune haemolytic anaemia. These antibodies are
cold agglutinins and often arise following atypical
pneumonia (due to Mycophma pneumoniae infection) or are associated with lymphoproliferative
disorders. Recent studies have shown that I antigen is
a glycoprotein consisting of at least six antigenic
determinants and that it is closely related to the
precursors of ABH and Lewis blood group substances.
One of these determinants has been characterized.
13. THE INTERACTION OF HYDROGEN IONS
AND CALCIUM IONS ON THE ATPase
ACTIVITY OF CARDIAC MYOFIBRILS
G. J. WILLIAMS,
M. R. STEPHENSand J. R. MUIR
Department of Cardiology, Welsh National School of
Medicine, Medical Teaching Centre, Heath Park,
Cardiff
The concentration of lactic acid rises in ischaemic
myocardium (Cornblatt, Ronelle, Parmeggioni &
Morgan, 1963, Journal of Biological Chemistry, 238,
1592; Williamson, 1966, Journal of Biological
Chemistry, 241, 5026) and it has therefore been
supposed that intracellular pH falls under these
conditions. Katz & Hecht (1969, American Journal of
Medicine, 47, 497) have suggested that the reduced
myocardial performance associated with ischaemia
is due to hydrogen ions competing with calcium ions
for binding sites on the regulatory protein, troponin.
Such competition would result in a reduction as the
pH fell in the number of active actin-myosin interactions at any given [&++] and therefore in the
myofibrillar ATPase activity and in the force of
contraction. Unfortunately experimental data on this
point is conflicting (Muhlrad & Hegyn, 1965, Biochimica et Bwphysica Acta, 105, 341 ; Schieller, 1967,
Pfliigers Archiv fur die gesamte Physiologie, 2%,70).
The interaction of [a++]
and [H+] on cardiac
myofibrillar A T P m activity was therefore studied,
both [Ca+ +] and [H+]being accurately controlled by
L
1 7 ~
buffers. Myofibrils were prepared from left ventricles
of normal dogs by a standardized technique (Muir,
Weber & Olson, 1971, Biochimica et Biophysica Acta,
234, 199). ATPase activity was measured over a
pH range 6.5-7.4, the [Ca++I in each range varying
from zero to 1.5 x l o 4 M . It was not possible to
exceed this pH range as the buffering action of
EGTA for calcium is ineffective outside this range.
ATPase of dog cardiac myofibrils, and rabbit cardiac
myosin and actomyosin was also measured in the
absence of [Ca+1‘ over the pH range 6-9. In addition
the influence of pH on the K,ATP of cardiac myofibrils was studied.
In the absence of ionic calcium, myofibrillar,
myosin and actomyosin ATPase activities are
maximal at pH 8.0. In addition the myofibrillar
ATPase activity for any given calcium ion concentration is depressed by lowering the pH. However, the
effect of pH on the K,ATP ( 1 x
M) shows that
the inhibition is non-competitive.
These results suggest that a fall in intracellular pH
could reduce cardiac myofibrillar ATPase activity
but that the effect is probably complex, competition
between calcium and hydrogen ions for binding sites
on troponin being only one factor.
14. BIOCHEMICAL
STUDIES
ON
THE
CARRIER STATE IN THE LESCH-NYHAN
SYNDROME
R. 0. MCKERAN,T. M. ANDREWS,
A. HOWELL,
D. A.
GmBs and R. W. E. W A ~
Division of Inherited Metabolic Diseases, MRC
Clinical Research Centre, Warford Road, Harrow,
Middesex HA1 3UJ
The Lesch-Nyhan syndrome (choreoathetosis, compulsive self-mutilation, mental retardation and
excessive uric acid production) is associated with the
absence of detectable IMP: pyrophosphate phosphoribosyltransferase (EC 2.4.2.8.) from the patient’s
tissues (‘complete HGPRT deficiency’). Occasional
cases of severe gout with gross uricacid overproduction
and sometimes minor neuropsychiatric abnormalities
have very low levels of HGPRT activity (‘incomplete
HGPRT deficiency’). These two conditions are
genetically separate, although both are X-linked. The
female carriers of the complete HGPRT deficiency
have previously been identified by the mosaicism of
their fibroblasts in tissue culture. We have studied
presumed carriers of the complete and incomplete
HGPRT deficiencies in a search for additional and
more easily obtainable evidence for the presence
of two cell populations in these women. The following
tissues were studied in addition to fibroblasts: hair
follicles, phytohaemagglutinin stimulated lymphocytes, cultured bone marrow cells and jejunal mucosa
biopsies. Our findings confirm that hair follicles can be
used to assist the diagnosis of the carrier state for the