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Pure myofibrils were isolated from bovine heart by sucrose layer ultracentrifugation. Cardiac myofibrils thus prepared contained more protein as insoluble stroma than skeletal muscle. The insoluble stroma largely consisted of connectin, an elastic protein of muscle. The connectin content in cardiac myofibrils was about 18% of the total myofibrillar protein and was three times that in skeletal myofibrils. In view of the role of connectin as an elastic component of muscle, the abundance of connectin in cardiac myofibrils may be responsible for keeping myofibrils short at rest. This would account for the more effective tension generation in cardiac muscle on passive stretching due to blood inflow (Stirling's law).

Glycolipids are well known cell membrane components and play a role in several biological phenomena on the cell surface.1 As glycolipids are relatively minor components of cells, it is necessary to develop analytical methods for small amounts of samples. Mass spectrometry have proved to be powerful tools for this purpose. Electron impact and chemical ionization mass spectrometry provide good information on the structure of permethylated or permethylated and reduced glycolipids.2–4 However, these ionization methods require the derivatization of the sample, and the ion intensities of the high mass region are very weak and difficult to detect continuously during analysis. The recently introduced “soft ionization techniques” are successfully applied for the analyses of non-volatile and thermolabile compounds. These include field desorption (FD), fast atom bombardment (FAB) and secondary ion mass spectrometry (SI-MS). However only a few reports on the application of these new techniques for the analysis of glycolipids5–11 have been published.

Lipids were extracted from beef retina by chloroform-methanol (2∶1); the gangliosides were removed from the total lipid extract by partitioning into water and chromatographing on thin layer plates coated with silica gel. The analytical methods are described for estimating ganglioside components, i.e., N-acetyl neuraminic acid, hexoses, hexosamine, sphingosine and fatty acids, in the presence of silica gel. Major gangliosides present in beef retina have been tentatively identified as follows: a ganglioside containing two N-acetyl neuraminyl groups but no hexosamine; two gangliosides containing two N-acetyl neuraminyl groups and one hexosamine; and a ganglioside with three N-acetyl neuraminyl moieties and one hexosamine.

A mixture of UDP-(N-acetyl)glucosamine-114C and UDP-(N-acetyl)galactosamine-114C (7∶3) served as a substrate to demonstrate in young rat brain tissue the presence of enzymes which catalyzes the reactions: UDP-glcNAc⇌UDP-galNAc (E.C.5.1.3) and UDP-galNAc+ gal-glc-cer→ galNAc-gal-glc-cer+UDP. The glycolipid acceptor specificity was examined and preliminary kinetic data were obtained for the UDP-(N-acetyl)galactosamine: gal-glc-ceramide N-acetyl galactosamine transferase. The products of the reaction were identified. The relationship of this reaction to ganglioside biosynthesis is discussed.