N-acetyltryptophan (AT) and caprylic acid (Cap) are known to suppress the heat-induced aggregation of serum albumins. In this study, we examined the commonality of AT and Cap on the protein aggregation using hen egg-white lysozyme, ovalbumin, and bovine γ-globulin (BGG), as well as bovine and human serum albumin. AT and Cap as additives increased the unfolding temperatures of human and bovine albumins analyzed by far-UV circular dichroism. Both AT and Cap highly suppressed the heat-induced aggregation of BGG as well as albumins, while they enhanced the aggregation of lysozyme. In all cases, the addition of 100 mM ArgHCl showed no synergistic effects with AT or Cap in suppressing the aggregation of BGG. The small chemicals of AT and Cap will be useful additives toward the thermal stabilization of albumins and γ-globulin.

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We analyzed the role of the gene encoding GABA transaminase (gatA) in Aspergillus oryzae by gene disruption. The gatA-disrupted strain could not grow on minimal medium with GABA as the sole nitrogen source. These results indicate that gatA is essential for GABA metabolism in A. oryzae.

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