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1. Of four proteolytic enzymes isolated from autolysing Saccharomyces carlsbergensis, one is inactivated at about 45 degrees C, whereas the others are stable at 50 degrees C. pH optima for activity are from 3.0 to 8.0 but maximum stability is between pH6.0 and 6.5. All appear to be glycoproteins, the carbohydrate moiety containing glucose and mannose residues. 2. Lysed protoplasts of the same yeast release four proteolytic enzymes each of which have two pH optima at pH3.0 and 7.0 approximately. Compared with the enzymes from autolysed yeast, resistance to high temperature is much less, and they are not glycoprotein in nature. 3. The same yeast grown with N-acetyltyrosine ethyl ester as nitrogen source secretes into the medium four proteases believed to be glycoprotein in nature. Generally they resemble the enzymes from lysed protoplasts more than those from autolysing yeast.

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S U M M A R YThe mole fraction of guanine plus cytosine in the DNA from Obesunzbacterium proteus was 48 %, similar to that of Hafnia alvei, Salmonella gallinarum and the RM bacterium. DNA: DNA competition studies indicated that 0. proteus strains fall into two groups, both of which could reasonably be included in the family Enterobacteriaceae. The same two groups were apparent from a numerical taxonomic investigation of 19 0. proteus strains which included 16 brewery isolates. The simple matching coefficients (%S) were calculated from results of 50 biochemical and taxonomic tests, and a dendrogram was constructed. Every 0. proteus isolate had the characteristics of the family Enterobacteriaceae. The two subgroups united at 86 % S, and formed a cluster with Hafnia and Salmonella strains at 72.5 % S. The difference between Hafnia alvei and 0. proteus was almost entirely due to their different vigour rating. Furthermore, in a simulated brewery fermentation, two strains of H. alvei grew in a mixed culture with yeast. This was originally the defining characteristic of the genus Obesumbacterium.We propose that reference to the genus Obesumbacterium should be discontinued, and that 0. proteus should be placed in the genus Hafnia as Hafniaprotea comb. nov.