rent construct now gives holoenzyme levels of 3- 
4% of total protein. As a part of this project, the 
cysG gene has been identified and sequenced. 
II. Regulation of 5-Adenosylmethionine Metabolism. 
Previously reported studies from Dr. Kredich's 
laboratory showed that human lymphocyte 5-ad- 
enosylmethionine synthetase is composed of non- 
identical subunits. Immunologic and enzymatic 
studies now indicate that the a-subunit is catalytic 
and that the function of the (3-subunit may be regu- 
latory. Attempts are now under way to clone the 
PUBLICATIONS 
genes for both subunits as part of an overall effort 
to characterize the different roles of these subunits 
and their expression in different cell types. cDNA 
for the hepatic enzyme from rat has already been 
cloned and sequenced in Dr. Kredich's laboratory 
Comparison of its sequence to those of the £. coli 
and yeast enzymes reveals a high degree of identity 
Comparison of the primary structures of the he- 
patic and lymphocyte enzymes will help explain the 
marked kinetic difference between these enzymes. 
Dr. Kredich is Professor of Medicine and of Bio- 
chemistry at Duke University Medical Center. 
Books and Chapters of Books 
Kredich, N.M., and Hershfield, M.S. 1989. Immunodeficiency diseases caused by adenosine deaminase defi- 
ciency and purine nucleoside phosphorylase deficiency. In The Metabolic Basis of Inherited Disease 
(Scriver, C.R., Beaudet, A.L. , Sly WS., and Valle, D. , Eds.). New York: McGraw-Hill, pp 1045-1075. 
Articles 
German, D.C., Kredich, N.M., and Bjornsson, T.D. 1989. Oral dipyridamole increases plasma adenosine levels 
in human beings. Clin Pharmacol Ther 45:80-84. 
Ostrowski, J., and Kredich, N.M. 1989. Molecular characterization of the cysJIH promoters of Salmonella 
typhimurium and Escherichia coli: regulation by cysB protein and A^-acetyl-L-serine. J Bacteriol 171:130- 
140. 
Ostrowski, J., Wu, J.-Y, Rueger, D.C., Miller, B.E., Siegel, L.M., and Kredich, N.M. 1989. Characterization of 
the cysJIH regions of Salmonella typhimurium and Escherichia coli B. DNA sequences of cysl and cysH 
and a model for the siroheme-Fe4S4 active center of sulfite reductase hemoprotein based on amino acid 
homology with spinach nitrite reductase. J Biol Chem 264.151 26-151 ii7 . 
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