Carbonic anhydrase in the sarcoplasmic reticulum of rabbit skeletal muscle.

Abstract

SUMMARY1. Sarcoplasmic reticulum vesicles and mitochondria were prepared from red and white skeletal muscles of the rabbit. The preparations were characterized in terms of their specific activities of citrate synthase, basal (Mg2+-dependent) and Ca2+-dependent ATPase (the latter two in the presence of NaN3 and ouabain), and their specific carbonic anhydrase activities were determined.2. Skeletal muscle mitochondria had high specific activities of citrate synthase (700-1200 mu. mg protein-1) and low carbonic anhydrase activities (0 1-0 4 u. ml mg protein-1). The latter are likely to be due to a contamination of the preparations with sarcoplasmic reticulum (s.r.)3. Preparations of s.r. vesicles showed negligible activities of citrate synthase and the expected differing patterns of basal and Ca2+-dependent ATPase in red and white muscles. Specific carbonic anhydrase activities in s.r. from both muscle types were high (2-4 u. ml mg protein-'). The highest carbonic anhydrase activity, 11 u. ml mg protein-1, was found in s.r. from rabbit m. masseter. The inhibition constant of s.r. carbonic anhydrase towards acetazolamide was 4-6 x 10-8 M and similar but not identical to that of cytosolic carbonic anhydrase II.4. It appears possible that the carbonic anhydrase II-like enzyme previously found by us in muscle homogenates (Siffert & Gros, 1982) originates from the s.r.5. Histochemical studies using the dansylsuphonamide method described previously (Dermietzel, Leibstein, Siffert, Zamboglou & Gros, 1985) showed an intracellular pattern of carbonic anhydrase staining compatible with the presence of the enzyme in s.r.: spots homogeneously distributed across the fibre crosssections in transversely sectioned fibres and thin, longitudinally oriented, bands in longitudinally sectioned fibres.6. It is estimated that s.r. carbonic anhydrase accelerates C02 hydration within the s.r. approximately 1000-fold. Thus, CO2 and HCO3-react fast enough to provide a rapid source and sink for protons leaving and entering the s.r. in exchange for Ca2+.

Inhibition of muscle carbonic anhydrase slows the Ca2+ transient in rat skeletal muscle fibers

“…Estimations of inhibition and catalysis constants revealed different properties of the CA of SR vesicle fractions and CA of SL vesicles and confirmed the existence of two membrane-bound CAs in muscle (41). Histochemical studies with the fluorescent CA inhibitor dimethylaminonaphthalene-5-sulfonamide (3,7) and immunoelectron microscopic studies with ultrathin sections (6) demonstrated an intracellular staining pattern, which is compatible with a CA associated with the SR membrane. In a previous study, we reported that inhibition of this SR-CA leads to significant changes in single twitches of fiber bundles of the soleus (SOL) and extensor digitorum longus (EDL) from rats (45).…”

“…6). However, the CO 2 -HCO 3 Ϫ system can fulfill this task only when it is catalyzed by CA, because the half-time of the uncatalyzed reaction of ϳ7 s is far too slow in view of the fast kinetics of Ca 2ϩ fluxes. Ca 2ϩ release lasts ϳ20-50 ms, and Ca 2ϩ reuptake lasts ϳ200-300 ms (Fig.…”

Carbonic anhydrase activity and biomineralization process in embryos, larvae and adult blue mussels Mytilus edulis L.

“…The activity of CA was measured by a micromethod developed by Maren (1960) and modified by Bruns et al (1986). The activity (A) of CA was expressed by the uncatalysed reaction time (t 0 ) and the catalysed reaction time (t enz ), using the following equation: A=(t 0 /t enz )-1.…”

Hypoxic incubation leads to concerted changes of carbonic anhydrase activity and 2.3 DPG concentration of chick embryo red cells

“…Packed red cells were either processed immediately or stored in liquid nitrogen. Carbonic anhydrase activity was measured at 0°C using the method of Maren (1960) as modified by Bruns et al (1986). Activities are given as units/milliliter red blood cell.…”