Autophosphorylation of untrained and well-trained skeletal muscle myosin.
Earlier the autophosphorylation of myosin and the labile phosphate (P) content of rabbit skeletal muscle was reported [6, 7, 9]. The present paper describes that the endogeneous preformed P level in fresh preparation of exercised muscle is higher than that of untrained control one. It was revealed that the presence of a significant amount of mitochondrial myosin (with much higher P content) in the well-trained human muscle preparations falsified the appreciation of myofibrillar myosin. Therefore, a reliable myofibrillar preparation with correct P content from exercised subjects was obtained only after the separation of mitochondrial fraction. The P content of fresh preparations can be increased by phosphorylation even in the exercised muscle myosins up to the most higher level in human samples. The phosphoryl group incorporation from [gamma-32P]ATP into the rabbit and hare myosins was checked by radioactive tracer technique, and confirmed by total P content determination performed parallel with molybdate test. It was stated that under present circumstances the labelled 32P incorporation was lower even at an optimal substrate concentration than that of P value obtained directly with molybdate method; because the total P content of preparations had not exchanged during 2 min incubation. So it has been concluded from [gamma-23P] phosphoryl group assayments that much higher amount of P was incorporated into P-Arg, N pi-P-His and fraction 2 as compared with unappreciated labelled P level of the inorganic P (P-Ser, P-Thr), P-Lys, N tau-P-His and minor fractions. From these observations it has been considered that the P-Arg, N pi-P-His and fraction 2 take part in the contraction mechanism and in the course of physical training.
Second Institute of Biochemistry, Semmelweis University Medical School, Budapest, Hungary.
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Fazekas
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Berentey
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Györgyi
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Székessy-Hermann
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D009132:Muscles / Q000201:enzymology*; D009218:Myosins / Q000378:metabolism*; D010710:Phosphates / Q000032:analysis; D010766:Phosphorylation; D011817:Rabbits
D010710:Phosphates; D000255:Adenosine Triphosphate; D009218:Myosins