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Muscle Fiber

Posted By: Joe Ames
Date: Thursday, May 11, 2000 at 3:43 p.m.

Muscle Fiber

Muscle is made up of fibers which are several centimeters long and measure 0.01 - 0.1 mm in diameter. The fibers are enclosed in membranes called Sarcolemma and are arranged in bundles which enclose fat and connective tissue. The fibers are cross-striated and this is due to the presence of cross-striated myofibrils. The myofibrils are embedded in the cell cytoplasm called sarcoplasm. The fibers contain peripherally distributed nuclei and a diagram of the arrangement of the various constituents of a muscle fiber is shown above. In addition to the constituents mentioned, the muscle fibers contain other components including mitochondria, ribosomes, lysomes and glycogen granules. The fibers make up the largest part of the muscle volume, but there is from 12-18% of extracellular space.

Meat contains three general types of proteins, the soluble proteins which can easily be removed by extraction with weak salt solutions, the contractile proteins and the stromaproteins of the connective tissue. The soluble proteins are classed as myogens and myoalbumins. The myogens are a heterogeneous group of metabolic enzymes. After extraction of the soluble proteins, the fibril and stroma proteins remain. They can be extracted with 0.6M potassium chloride to yield a viscous gel of actomyosin.

Myosin is the most abundant of the muscle proteins and makes up about 38% of the total.

Myosin has enzyme activity and can split ATP (Adenosine triphosphate) into ADP (Andenosine diphosphate) and monophosphate, thereby liberating energy which is used in muscle contraction. The myosin molecule is not a single entity. It can be separated into two subunits by means of enzymes.

Actin makes up about 13% of the muscle protein so that the actin-myosin ratio is about 1:3. Actomyosin is a complex of F-actin and myosin, and is responsible for muscle contraction and relaxation. Contraction occurs when myosin ATP-ase activity splits ATP to form phosphorylated actin and ADP.. Relaxation of muscle depends on regeneration of ATP from ADP by phosphorylation from creatine phosphate.

Principles of food chemistry
by John M. deMan Ph.D.


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