Perhaps of some help...
Marilyn

http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=292827&action=stream&b
lobtype=pdf

Insulin Secretion in Response to Protein Ingestion *
JOHN C. FLOYD, JR.,t STEFAN S. FAJANS, JEROME \V. CONN, RALPH F. KNOPF,
AND JUAN RULL
(From the Department of Internal Medicine, Division of Endocrinology and
Metabolism awd
the Metabolism Research Unit, the University of Michigan, Ann Arbor, Mich.')

[...]

Summary

Protein meals were fed to healthy subjects, and concentrations of plasma
insulin, leucine, amino nitrogen, free fatty acids, and blood glucose were
determined. Plasma insulin, leucine, and amino
nitrogen increased significantly during each test in which they were
measured. Mean concentrations of plasma free fatty acids decreased. Mean
blood glucose concentration did not change, although decreases were observed
in one-third of the tests. Pretreatment of some subjects with
chlor-propamide failed to modify the changes in blood glucose and plasma
free fatty acids observed in the absence of such pretreatment.

The increases in plasma insulin after the ingestion of the protein meals
were considerably greater than those that would have been expected to result
from the modest increases observed in plasma leucine. These findings suggest
that amino acids other than leucine, or amino acids in combination with
leucine, induced the release of insulin.

We conclude that 1) ingestion of protein meals results in significant
increases in plasma insulin, 2) these increases in plasma insulin cannot be
accounted for solely or even largely by the effect of l-leucine contained in
the meals, and 3) ingestion of protein and rising plasma levels of certain
amino acids appear to be associated with a physiologic stimulus for insulin
release.

We speculate that the purpose of the insulogenic response to protein
ingestion is to aid both in the utilization of absorbed amino acids and in
their synthesis to protein.