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chapter 11

Heteropolysaccharides II: Proteoglycans and Peptidoglycans

I

FIGURE 11-10

Formation and function of lysosomes. Lysosomal enzymes are synthesized in the rough endoplasmic reticulum. Those

with appropriate recognition markers are processed and packaged into primary lysosomes in the complex network of the

Golgi apparatus. 1, 2, and 3 represent digestion of extracellular substance segregated into a heterophagosome; 1,4, and

5, digestion of segregated cytoplasmic material (autophagosome); 1

and

6

, extrusion of lysosomal enzymes that will act

extracellularly (e.g., collagenase); and 7, a residual body. [Reproduced with permission from L. C. Junqueira, J. Carneiro,

and J. L. Long,

B a sic H isto lo g y,

5th ed. Appleton & Lange, Norwalk, CT, 1986. ©1986 Appleton-Century-Crofts.]

cornea. Types IH, II, III, and VIII are characterized by

severe mental retardation, while types IS, IV, and VI

exhibit normal intelligence. Patients with different en-

zyme deficiencies may exhibit phenotypic similarities

(pleiotropism), and they may also exhibit variation in

clinical severity with the same enzyme deficiency (al-

lelic variants). The enzyme deficiency can be estab-

lished by assays on peripheral lymphocytes or cultured

fibroblasts. Prenatal diagnosis is possible but requires

successful culture of amniotic fluid cells and assay of

specific enzymes. No specific therapy is available. Man-

agement focuses on providing prognostic information and

counseling.

11.2 Peptidoglycans

Peptidoglycans are components of bacterial cell walls

and consist of heteropolysaccharide chains cross-linked

by short peptide chains. These cell walls bear the anti-

genic determinants; when exposed to them, humans (and

other mammalian species) develop specific antibodies to

defend against bacteria. Bacterial virulence is also related

to substances associated with the cell wall. Cell wall syn-

thesis is the target for the action of the penicillins and

cephalosporins.

Bacterial cell walls are rigid and complex, enable the

cells to withstand severe osmotic shock, and survive in a