
insulin and protein metabolism
the present status of protein synthesis within cells has
been outlined.  protein is formed in the absence of insulin;
the net formation of protein is accelerated by insulin.  the
effects of insulin on protein metabolism take place independently
of the transport of glucose or amino acids into the
cell; of glycogen synthesis; and of the stimulation of high
energy phosphate formation.  in the case of protein metabolism,
as in certain studies on the pathways of glucose and
fat metabolism, these observations reveal striking intracellular
effects of insulin in many tissues.  within most
tissues the effect of insulin appears to find expression predominantly
at the microsomal level.  incidentally, other
hormones which affect protein metabolism such as growth
or sex hormones appear to act at the microsomes.  the fact
that insulin exerts effects on protein metabolism at other
intracellular sites as well as the above independent effects
leads one to agree that its action consists of a stimulation
of multiple, seemingly unrelated, metabolic events.
the fact that an immediate effect of insulin on protein
synthesis is independent of the immediate need for extracellular
glucose or amino acids does not mean that the
sustained functioning of cells is likewise independent.  the
biochemist is fully aware of metabolic defects in diabetes
which are not altered by insulin in vitro, but which demand
varying periods of pretreatment of the animal.  it is
also known that in diabetes some proteins (enzymes) may
be deficient while others may be produced in excess in the
absence of insulin.
it is suggested that the physician desires at least two
kinds of relation between these fundamental studies and his
patients.  one is the possible relation of a deficiency of insulin
action to pathological processes in tissues which have
not as yet been examined by the methods described.  the
other is the need for more accurate measurements of the
metabolic disorder and its control than such things as
urinary and blood glucose.  in developing such future improvements,
the place of insulin in protein biosynthesis
must be kept in mind.
