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The phospholipids of pork longissirnus dorsi muscle were investigated. The proportions of the major phospholipid components appeared to be constant in different regions of the same muscle, although the total lipid-P varied widely.Homogenates of the muscle were fractionated by differential centrifuging -'myofibrillar', 'mitochondria]', 'reticular', and 'final supernatant' muscle fractions being obtained. Sarcoplasmic reticulum appeared to be present very largely with the fibrils in the 'myofibrillar' fraction, which contained 40-78% of the total lipid-P. The percentage composition of the phospholipids was similar in the first three subcellular fractions, while the fourth contained less of the 'kephalin' component. During fractionation of the muscle, substantial losses of .phospholipids occurred; the possible origin and cause of these losses are discussed.The sum of lipid-P in the first and third subcellular fractions, containing sarcoplasmic reticulum, showed a highly significant negative correlation with PHI, (muscle pH 45 minutes after slaughter) which represents an approximate index of the rate of post-mortem glycolysis in the muscle. The significance of this correlation is discussed.

SUMMARY –Calcium uptake and Ca2+‐activated ATPase activity have been investigated in relation to pH, in pork muscle Longissimus dorsi, sampled 35 min postmortem. Both the rate of calcium uptake and the enzyme activity were negatively, and significantly, correlated with pH1, except when the latter value dropped below 5.9. At pH1 < 5.9, impairment of reticular function and of enzyme activity became apparent. As pH1 is a guide to the rate of postmortem glycolysis, the significance of the findings is discussed with respect to accelerated glycolysis and the development of the PSE condition in pork.

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