Experimental allergic aspermatogenic orchitis. II. Some chemical properties of the API protein of the sperm acrosome

Abstract

The APl protein, a unique aspermatogenic protein localized in the sperm acrosome, exists as a single polypeptide chain of 136 amino acids, as shown by a single band on gel electophoresis in sodium dodecyl sulfate and the recovery of the expected 21 to 22 tryptic peptides on peptide mapping. The APl protein appears to exist in a compact, highly stable conformation, as shown by its resistance to trypsin hydrolysis. Its aspermatogenic activity is not affected by trypsin treatment, by heating at 99 °C for 1 h, by 8 M urea, or by acid conditions. After reduction and alkylation, however, the molecule appears to open up, since it becomes hydrolyzable by trypsin and migrates more slowly on gel electrophoresis at pH 2.7 and 8.6. After alkylation, the APl protein still migrates as a single band at pH 2.7. The APl protein shows microheterogeneity near its isolectric point at pH 8.6; each of five bands shows the same amino acid analysis. Aggregation was not observed following treatment with dimethylsuberimidate. The molecular weight of 15 000, obtained from gel electrophoresis consists of 136 amino acids with a relatively high content of proline, half cystine, glycine, histidine and tryptophan. No galactose, mannose, fucose, glucose, or hexosamines were found; the APl protein is thus not a glycoprotein.