Effectors of purified adenyl cyclase from Streptococcus salivarius |
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Authors: | R L Khandelwal I R Hamilton |
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Affiliation: | 1. Chongqing University, College of Electrical Engineering, Chongqing 400030, China;2. Department of Mechanical Engineering, Department of Bioengineering, University of California Berkeley, CA 94720, USA;3. Department of Endocrinology, Luoyang Central Hospital Affiliated to Zhengzhou University, Luoyang 471009, China |
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Abstract: | The activity of highly purified (3200-fold) adenyl cyclase from Streptococcus salivarius was examined in the presence and absence of Pi, inorganic pyrophosphate, nucleotides and glycolytic intermediates. The enzyme was inhibited by Pi, ADP and all the triphosphates and monophosphates of guanosine, uridine, inosine and cytidine; inhibition was completely competitive. The inhibition in the presence of PPi was partially competitive, while AMP produced inhibition of the mixed type, i.e., partially competitive and completely noncompetitive. PPi was the most potent inhibitor (Ki = 0.23 mm) followed by ADP (Ki = 0.43 mm), GTP (Ki = 0.52 mm) and UTP (Ki = 0.60 mm). Severe inhibition of the enzyme was also observed in the presence of the diphosphate and sugar nucleotides of the above bases at concentrations between 0.1 and 5 mm, when tested at one substrate concentration (ATP = 0.6 mm). The respective cyclic 3′,5′-nucleoside monophosphates were, however, only slightly inhibitory (maximum 11%).While the nucleotides were generally inhibitory, the activity of the enzyme was variable in the presence of various glycolytic intermediates. Weak activation of adenyl cyclase activity was observed with glucose-6-P, glucose-1-P, 2-P-glycerate and pyruvate. 2-P-glycerate required the lowest concentration for half maximal activation (Ka = 0.13 mm) followed by glucose-1-P (0.24 mm), glucose-6-P (0.55 mm) and pyruvate (1.12 mm). These compounds increased the V of the enzyme without affecting the apparent Km for ATP. Fructose-6-P, fructose-1,6-P2, glyceraldehyde-3-P and P-enolpyruvate inhibited or activated the enzyme depending upon the concentration of the compound used. Both the apparent Km for ATP as well as the V were altered by fructose-6-P and fructose-1,6-P2. However, activating concentrations of glyceraldehyde-3-P and P-enolpyruvate increased the V without affecting the apparent Km, whereas inhibiting concentrations decreased the V and increased the Km for the substrate. |
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