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(i) Myosin from chicken gizzards was purified by a modification of an earlier procedure ( M. N. Malik, 1978, Biochemistry 17 , 27–32). When this myosin, as well as that prepared by the method of A. Sobieszek and R. D. Bremel (1975, Eur. J. Biochem. 55 , 49–60), was analyzed by gradient slab gel using the discontinuous buffer system of Neville (1971, J. Biol. Chem. 246 , 6328–6334), a closely spaced doublet in the heavy chain and four light chains were observed as opposed to one heavy chain and two light chains with the method of Weber and Osborn (1969, J. Biol. Chem. 244 , 4406–4412). These findings raise the possibility of the existence of myosin isoenzymes in smooth muscle. (ii) The purified gizzard myosin was found to be free of kinase and phosphatase. Phosphorylation or thiophosphorylation of myosin was observed only by exogenously adding kinase. A maximum of 1.2 mol of 32 P/mol of myosin and 2.3 mol of 35 S/mol of myosin were obtained. The actin-activated ATPase activity depended upon the extent of thiophosphorylation of myosin; a four- to fivefold increase in the activity was observed when myosin was fully thiophosphorylated. Thiophosphorylated myosin was found to be more stable than phosphorylated myosin.

(i) The steady-state kinetic data obtained with purified gizzard and uterus smooth muscle myosins indicated the presence of a plateau region on the substrate-saturation curves. Hill plots of these data provided evidence for mixed positive and negative cooperative interactions. In contrast, when gizzard myosin was prepared according to the method of A. Sobieszek and R.D. Bremel (1975, Eur. J. Biochem. 55 , 49–60), the saturation curve in the presence of CaATP was hyperbolic and no cooperativity of the binding site(s) was discerned. However, in the presence of MgATP although the curve appeared hyperbolic the Hill plot of the data was biphasic with negative cooperativity at low MgATP concentration, (ii) When thiophosphorylated gizzard myosin was used for kinetic analysis, the plateau region in the presence of MnATP was eliminated from the saturation curve and this curve became hyperbolic. However, in the presence of MgATP, although the plateau was almost eliminated, the saturation curve was still biphasic with either no or greatly reduced negative cooperativity of binding sites at low MgATP concentrations but positive cooperativity of binding at high MgATP concentrations. In addition, the thiophosphorylation of myosin also increased the K m and V of MgATP and MnATP, thus indicating weaker affinity for these substrates with thiophosphorylated myosin. (iii) Gizzard myosin also hydrolyzed other nucleotides (the order of rates being CTP = ITP > ATP = UTP > GTP), therefore saturation kinetics using different nucleotides as substrates was also carried out. The saturation curves with each nucleotide were different i.e., hyperbolic with CTP, sigmoid with GTP, hyperbolic with biphasic Hill plot with ITP, and possessing plateau with UTP. In addition, it was observed that the kinetic pattern with each nucleotide was very sensitive to temperature and pH.

Three hundred thirty-three 5-week-old male Swiss albino mice divided into 11 equal groups in four experiments were inoculated with single graded doses of Trichinella spiralis larvae. Doses ranged from 400 to 51,200 larvae per mouse. Within the limits of these experiments, (1) the number of deaths among mice infected with increasing numbers of larvae increased until a mortality of one hundred per cent (100%) was reached. (2) Mean and median survival times varied inversely with the size of the inoculum. (3) There was no assurance that mean survival times for groups of homogeneous mice inoculated with equal dosages in different experiments would be comparable or precisely predictable.