A hypocalcemic and lympnocyte-stimulating substance isolated from thymus extracts, and its physicochemical properties

Two kinds of active protein fraction, TP1 and TP2, were isolated from bovine thymus extracts. Both these fractions showed a single band in polyacrylamide gel disc electrophoresis. Though these two fractions showed a difference in potency, they both lowered serum calcium in rabbits and increased lymphocytes in mice. Molecular weight determination by SDS polyacrylamide gel electrophoresis gave the values of 68,000 for TP1 and 57,000 for TP2. Amino acid composition of TP1 did not show marked characteristics but was clearly different from that of bovine serum albumin. Isoelectric focusing showed the isoelectric point at pH 5.65 for TP1 and pH 5.4 for TP2. Dose-response relation in serum calcium-lowering activity was examined with a sample purified from the extracts, and a linear dependence of the response to log dose was recognized over a moderate range of doses. The time-course measurement of the hypocalcemic activity showed that the action of TP1 is somewhat different from that of calcitonin.