Differential coupling of smooth and skeletal muscle pyruvate kinase to creatine kinase

The interaction of pyruvate kinase from skeletal (SKPK) and smooth (SMPK) m uscle with MM-creatine kinase (MMCK) and BB-creatine kinase (BBCK) was asse ssed using temporal absorbance changes, variations in absorbance at differe nt wavelengths, concentration dependence, association in an electric field, and PK kinetic activity. SKPK exhibits a time course of absorbance increas e in the presence of MMCK with a time constant of 29.5 min. This increase o ccurs at all wavelength from 240 to 1000 nm. At 195 nm, the combination of SKPK and MMCK produces: a decrease in absorption with electric fields of bo th 0 and 204 V/cm. The change in SKPK-MMCK is saturable. SKPK activity is s ignificantly increased by the presence of MMCK in solutions of 0-32% ethano l. These results indicate specific SKPK-MMCK interaction. SMPK and BBCK did not exhibit similar coupling when the BBCK concentration dependence of abs orbance or SMPK activity in solutions of 0-32% ethanol was determined. Both MMCK and BBCK increased SKPK activity; neither MMCK nor BBCK increased SMP K activity. The ability to form diazymatic complexes with creatine kinase a ppears;to reside in SKPK. This coupling may account for the increased flux through PK without significant substrate changes seen during skeletal muscl e activation. This coupling will not occur in smooth muscle.