A RIA has been developed for somatomedin A (SM-A) utilizing Sepharose-bound antibodies. This assay, measuring SM-A, the insulin-like growth factors 1 and 2, and somatomedin C, allows determination in serum samples. In comparison with a serum standard, the mean serum levels in patients with acromegaly or GH deficiency and healthy subjects were 8.7 %/- 0.7 (n = 25), 0.24 +/- 0.02 (n = 25), and 1.15 +/- 0.11 U/ml, respectively. The correlation coefficient between immunoreactive SM-A and SM-A by radioreceptor assay was highly significant (r = 0.93), although the potency ratio of SM-A between the two groups of patients was higher in the RIA than in the radioreceptor assay. Gel chromatography revealed that SM-A in acromegalic serum is bound to a carrier protein which is absent in patients with GH deficiency. After gel chromatography at low pH, 90% of applied immunoreactive SM-A was recovered in the low molecular weight fraction and consisted mainly of neutral polypeptides.

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lower yields. Coupling yields increased strongly with increase in the light intensity. The possible specificity of the coupling was investigated in the bovine serum albumin-fluorescein system since bovine serum albumin is known to contain binding sites having affinity for fluorescein. Tryptic digestion of the albumin-fluorescein adduct followed by separation of the peptides mainly yielded one labeled tripeptide. The sequence was found to be X-Leu-Tyr where X is the residue containing the fluorescein label. A comparison with the known parts of the bovine serum albumin sequence indicates that it is identical with a sequence Tyr-Leu-Tyr found about 130 residues from the N-terminal end close to one of the two tryptophans in the protein. It is possible that photoinduced coupling can be used as a general method for affinity labeling. fee ted. However, under the conditions normally used for dye-sensitized photooxidation no coupling takes place and only destruction or modification of certain amino acid residues occurs.

Prolonged heat treatment of solutions of human serum albumin at 60°C resulted in formation of one aggregate fraction and one fraction that was stable against further heat treatment. Fatty acid analyses on these fractions indicate that the heat stable fraction is formed by migration of fatty acids from the aggregating molecules to the remaining monomer thereby stabilizing the latter against heat denaturation. Disulphide and SH groups are involved in the aggregation process.