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Papain and insoluble cellulose-papain have been employed to digest myosin. The slow-sedimenting peak of papain-digested myosin is much larger than that of trypsin digests, indicating the presence of more than light meromyosin (LMM) in this peak. The papain heavy meromyosin (HMM) has a weight-average molecular weight between 115,000 and 140,000, indicating degradation to monomeric subfragments. A minor slow peak is present in papain HMM preparations, and the relative amount of the major fast peak is often diminished upon raising the pH or ionic strength. Ultraviolet optical rotatory dispersion measurements suggest that this process is accompanied by a loss of helical content. Possible explanations for the heterogeneity T X he action of proteolytic enzymes such as trypsin and chymotrypsin on myosin involves a cleavage of the myosin molecule into two fragments (Perry, 1951;Gergely, 1953;Mihalyi and Szent-Gyorgyi, 1953). The smaller fragment, light meromyosin (LMM),* 1 exhibits solubility characteristics similar to myosin. The larger fragment, heavy meromyosin (HMM), retains the adenosine triphosphatase (ATPase) activity of the parent molecule as well as its ability to combine with actin, and is soluble in low ionic strength solutions. Recently Mueller and Perry (1962) have demonstrated that further digestion of HMM with a high concentration of trypsin releases a smaller enzymatically active subfragment. While it is well established that papain splits 7-globulin into fragments retaining the ability to combine with antigen (Porter, 1958), the action of papain on myosin has not yet been reported.A novel approach to the study of the action of enzymes on substrates has been introduced by Bar-Eli and Katchalski (1960), who have bound various enzymes to water-insoluble carriers through covalent linkages. The use of cellulose as a supporting medium •From the

Magnesium deficiency is generally associated with an impaired ability to dispose of glucose. In order to test whether or not increasing the peripheral free Mg concentration ([Mg 2+ ]) would enhance glucose disposal, we have carried out glucose infusions in sheep with and without simultaneous infusion of Mg. Basal plasma glucose levels were higher in lactating sheep ('lactators') than in non-lactating sheep (controls) (P < 0.05). The glucose disposal rate (K G ) with no added Mg was greater in lactators than controls (P < 0.05). When Mg was added to the infusate, K G in lactators was reduced (P < 0.005). Infusion of Mg depressed basal insulin levels in controls and lactators (P < 0.0001 for both). The insulin response to the intravenous glucose tolerance test (IVGTT) was lower in lactators compared with controls (P < 0.0001); however, after correcting for the reduced basal insulin level when Mg was included during the IVGTT, there was no difference between the two groups. We conclude that intravenous Mg at the doses used in this study leads to a decrease in basal insulin secretion, and that increasing serum

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