AJP - Renal Physiology, Vol 250, Issue 4 649-F658, Copyright © 1986 by American Physiological Society
Serine synthesis in rat kidney: studies with perfused kidney and cortical tubules
M. Lowry, D. E. Hall and J. T. Brosnan
Renal serine synthesis was studied in the isolated perfused kidney and in
isolated cortical tubules. Serine was produced by the perfused kidney from
both glycine and aspartate, indicating flux through at least two separate
pathways: serine hydroxymethyltransferase and either the nonphosphorylated
or phosphorylated intermediate pathways. The precise nephron site of serine
production was determined by measuring serine synthesis from various
precursors and the activities of enzymes of both pathways in isolated
tubules fractionated on a Percoll gradient into proximal tubule and distal
tubule fractions. Both pathways of serine synthesis were located in
proximal tubules. Detailed studies of serine synthesis from glycine
demonstrated extremely tight coupling between the glycine cleavage enzyme
and serine hydroxymethyltransferase, since the rate of 14CO2 production
from [2-14C]glycine was less than 5% of that of [1-14C]glycine, whereas the
rate of incorporation of 14C into serine from [2-14C]glycine was double
that from [1-14C]glycine. These studies demonstrate that the kidney can
synthesize serine by two separate pathways, both located in the cells of
the proximal tubule.
