ATP-dependent and -independent Protein Degradation in Extracts of the Psychrotrophic Bacterium Authrobacter sp. S1 55

Abstract

Proteolysis of endogenous and exogenous substrates in cell-free extracts of the psychrotrophic bacterium Arthrobacter sp. S, 55 has been compared. Endogenous proteins were degraded only after treatment with cyanogen bromide. The hydrolysis of exogenous proteins of high M , (i.e. casein) was optimum at alkaline pH and was stimulated by Cat+, Mg2+, Mn2+ and ATP. The serine protease inhibitor phenylmethylsulphonyl fluoride had no effect on ATP stimulation. Small peptides (i.e. insulin) were degraded at very high rates. This activity was optimum at slightly acidic pH and was stimulated by Ca2+, strongly inhibited by Mn*+, but not affected by ATP. Degradation of cyanogen bromide-treated cellular proteins displayed two pH optima which corresponded to the optimum pH for the degradation of insulin and casein. The characteristics of these acidic and alkaline activities were identical to those active against insulin and casein respectively. The proteases which degraded casein were much more heat resistant than those which degraded insulin.Abbreviations : PHMB, p-hydroxymercuribenzoate; PMSF, phenylmethylsulphonyl fluoride. 0001-4075 0 1987 SGM

Purification and Characterization of a Catalase from the Facultatively Psychrophilic Bacterium Vibrio rumoiensis S-1 T Exhibiting High Catalase Activity

“…From molecular evolution and diversity points of view, thermoinstability may be important in order to sustain the metabolism of organisms growing in cold temperatures because thermoinstability may be in accordance with low-temperature-specific protein turnover. A low-temperature-specific proteolytic system has been described for the psychrophilic bacterium Arthrobacter globiformis SI55 (34,35). On the basis of our experimental results and previously reported examples of psychrophilic enzymes, it is considered that thermoinstability is one of the most fundamental features of the psychrophilic enzyme.…”

Lipase and acidic phosphatase from the psychrotrophic bacteriumPseudomonas fluorescens: Two enzymes whose synthesis is regulated by the growth temperature

“…It should be noted that in both cases, the low phophatase and lipolytic activities at 28°C, which is near the optimal growth temperature for this strain, cannot be completely accounted for by the decreased transcription of the corresponding gene. This suggests that an additional post-transcriptional control may exist: it could of course occur at several levels including increased turnover at 28°C [12]. The mere stability of the enzymes would not be the cause of this decrease, at least in the case of the lipase, whose stability is well documented [13].…”

Temperature-dependent changes in proteolytic activities and protein composition in the psychrotrophic bacterium Arthrobacter globiformis S155

“…Cells in exponential growth (500 ml) at 10, 20 or 32 "C were harvested by centrifugation at lOOOOg for 10min and the pellets were washed twice with fresh medium. Cells were broken by ultrasonic treatment either in buffer C ( 5 0 m~-Tris/HCl, pH 8, 10 m-CaC12, 10 m-MgCl,, 0-5 m~-D T T ) or in buffer I (50 mM-Tris/HCl, pH 6-5, 10 m-CaCl,, 0-5 ~M -D T T ) as previously described (Potier et al, 1987b). Unbroken cells were removed by centrifugation at 12OOOg for 10 min and the supernatants were used immediately to test proteolytic activities.…”

“…Proteolysis of casein and insulin in cell-free extracts of A. globiformis S155 is effected by enzymes with differences in pH optima, and in metal-ion requirements and sensitivities (Potier et al, 1987b). The proteolytic activities at 20 "C of extracts of cells grown at 10,20 and 32 "C were compared ( Table 1).…”